Partially rewrite switch_xml_set_attr to fix memory leaks, uninitialized
argument values and use-after free warnings from Clang static analyzer.

Fixes these problems:

 - Add some comments and a new variable such that the code can more
   easily be audited / understood.
 - Always clear SWITCH_XML_DUP flag even if an error occurred to prevent
   free()'ing static strings on future invocations.
 - Keep the attribute list in a consistent state even if one of the
   memory allocation fails.
 - Keep allocation metadata in a consistent state when shrinking of the
   attribute lists fails. Previously the metadata was not updated,
   resulting in a wrong mapping from attributes to allocation flags.
 - Fix memory leaks when allocations fail.

Previous behavior: invalid memory accesses are possible after a memory
allocation failure, previous attributes may be lost.
New behavior: attributes list is always valid, a new attribute is either
set (or not), attributes can always be removed.

FS-8400 [verto_communicator] Removing deprecated use of stream.stop(), removing unused code and making volume meter gray so we can see it in a white background

Merge pull request #581 in FS/freeswitch from ~JAONZE/freeswitch:feature/FS-8400-add-camera-and-microphone-preview to master

* commit '522547f8':
  FS-8400 [verto_communicator] Added Camera and microphone preview after the splash screen.

Merge pull request #579 in FS/freeswitch from ~MARCELO1337/freeswitch-fs-8415:feature/FS-8415-send-180-ringing-for-early-media to master

* commit '7c3aed29':
  FS-8415 #resolve [support early with 180 using early_use_180=true]

FS-8377 Fix the handling of hiredis limit release when using an interval. The expectation for interval is to NOT decrement the limit.

Merge pull request #578 in FS/freeswitch from ~MARKL/freeswitch:bugfix/FS-8413-segfault-calling-session-getvariable-nil to master

* commit '6288af5e':
  FS-8413: Segfault calling session:getVariable(nil) in lua script

script calling session:getVariable() with a null variable
name will cause FreeSWITCH to segfault.

This change checks whether varname parameter to
switch_channel_get_variable_dup is non-NULL.

* commit 'e96c2d49':
  FS-8411 Replace ping_frame with video_ping_frame in a couple places that were missed

Merge pull request #573 in FS/freeswitch from ~WTCROSS/freeswitch:bugfix/FS-8398-ubuntu-trusty-deb-packaging to master

* commit '21a79e3f':
  FS-8398: Added event_handlers/mod_amqp to avoided modules for Ubuntu 14.04 Trusty

Merge pull request #574 in FS/freeswitch from bugfix/FS-8154-segmentation-fault-occurs-while-eavesdropping to master

* commit 'b4045420':
  FS-8154 #resolve [Segmentation fault occurs while eavesdropping on video call]

This change makes it so that event_handlers/mod_amqp is avoided when building
debian packages for Ubuntu 14.04 (Trusty). If this module is packaged there is
a dependency issue related to the rabbitmq libraries.

Avoiding the module was the simplest solution to achieve debian packaging on the
Ubuntu 14.04 OS.

Merge pull request #570 in FS/freeswitch from ~JAONZE/freeswitch:bugfix/FS-8222-closing-screen-share-does-not-end to master

* commit '320cf0ad':
  Target link for the plugin url, added comment explaining override $.FSRTC callback
  FS-8222 [verto_communicator] updated getScreenId.js in order to detect plugin issues and attached an 'ended' event to screenshare stream in order to detect 'stop sharing' click

* commit 'e6ae2e9b':
  FS-8392: change rtpmap payload to a number in dynamic range to allow both H263 and H263+ to be offered

FS-8392: change rtpmap payload to a number in dynamic range to allow both H263 and H263+ to be offered

FS-8222 [verto_communicator] updated getScreenId.js in order to detect plugin issues and attached an 'ended' event to screenshare stream in order to detect 'stop sharing' click

Merge pull request #550 in FS/freeswitch from ~DRAGOS_OANCEA/freeswitch-dragos:opus-fec-fix to master

* commit '65fd0792':
  FS-8319: mod_opus: fix and cleanup of switch_opus_has_fec() and switch_opus_info().

Merge pull request #555 in FS/freeswitch from ~DRAGOS_OANCEA/freeswitch-dragos:opus-repacketization-toggle-fec to master

* commit 'd145111e':
  FS-8344: mod_opus: toggle FEC on the last frame which is to be packed, so that FEC will be only present on the first SILK frame of the next Opus frame (Opus repacketization).

Merge pull request #546 in FS/freeswitch from ~COREY BURKE/freeswitch:feature/FS-8281-expose-srtp-and-srtcp-crypto-keys to master

* commit '0316fdfc':
  FS-8281: Expose SRTP and SRTCP crypto keys as channel vars

New vars are srtp_{local,remote}_crypto_key and srtcp_{local,remote}_crypto_key.
Allows decrypting packet captured media streams for debugging.

Merge pull request #549 in FS/freeswitch from ~DRAGOS_OANCEA/freeswitch-dragos:opus-decoder-statistics to master

* commit 'ea65a31e':
  FS-8313: mod_opus: show decoder stats at end of call (how many times it did PLC or FEC)

* commit 'c3a59c4b':
  FS-8373 Improve quality of recordings when using fast encoding

* commit '216e79f7':
  FS-8380 Improve mod_av's handling of vw and vh core file params

FS-8370 #resolve [mod_rayo] found another place in <prompt> where a message was freed after being queued for delivery. This resulted in a freed object being serialized, crashing FS.