FS-11384: stun: fix for when parsing incoming packets that contain attributes with no value (like USE_CANDIDATE)

FS-11382: [core] add switch_pool_strip_whitespace function to strip whitespace using pool allocation

the timebase logic is tighed to code internal logic and cannot be changed externally

Merge pull request #1492 in FS/freeswitch from ~HUNYI/freeswitch:bugfix/FS-8579-broadcast-hold-bleg to master

* commit '554387c8':
  Skip holding b leg only if it is on hold

Merge pull request #1491 in FS/freeswitch from ~HUNYI/freeswitch:feature/FS-8900-improve-record_follow_transfer to master

* commit '069da397':
  Improve recording transfer

Merge pull request #1453 in FS/freeswitch from ~HUNYI/freeswitch:bugfix/FS-10826-fix-sample-rate to master

* commit '87d4a6a0':
  FS-10826 [core] Fix file handler sample rate after transfer

Merge pull request #1526 in FS/freeswitch from ~HUNYI/freeswitch:bugfix/FS-11176-fix-do-not-restore-previous-codec to master

* commit '227a1349':
  FS-11176: [core] do not use previous codec if its not ready

FS-11363 Fix unpredictable/random zoom, when camera's video aspect ratio (a/r) equal to conference layout's tile a/r

This reverts commit 0342762f.

Usually tiles recalculated when new image comes in, however when 'overlap' option is in effect - tiles recalculated multiple times.
And when layout also has 'zoom' option - when image recalculated it each round zooms itself deeper and deeper, until new images comes and image resets to proper state.
This looks like flicker.

The fix is to always take for zoom calculations real image dimensions instead of previously recalculated.

HOWEVER!
There are too many math and corner cases in mod_conference, so i propose it to be reviewed by widest audience of people who wrote mod_conference!

+ don't shoot in a leg and keep 'rtt_now' value correct (even if we clear it few lines after), because after some time it could be changed.

FS-11362 Rearrange poll() errors handling to properly report poll hangup. Handle and log case when client sent close request. Add errno to errors where applicable.

FS-11362 FS could close client verto connection due to incorrect handling of SSL function return values (when SSL layer need to communicate with client on its own, f.e. keys re-negotiation)

FS-11360 Fix FS degradation over time in DTLS layer (especially if outdoing packets rate higher that incoming)

When we handle DTLS layer in do_dtls() and there are no incoming packets yet - we still call BIO_write() with NULL buffer and it is an error and BIO_write() will stuck for a long time in libssl/libcrypto error subsystem.
(that also possibly relates to fact that libssl/libcrypto init/deinit/error-handling is broken in general in FS, however that is another big issue)

Merge pull request #1580 in FS/freeswitch from ~ANDYWOLK/freeswitch:bugfix/FS-11368-use-system-flite1 to master

* commit 'ccc23b78':
  FS-11368: [mod_flite] Use system flite1 instead of libflite

Merge pull request #1577 in FS/freeswitch from ~ANDYWOLK/freeswitch:FS-11361-switch-debian-packages-building to master

* commit 'f98da7d5':
  FS-11361: [Build-System] Switch Debian packages building script util.sh from jessie stable to stretch stable.

Merge pull request #1579 in FS/freeswitch from ~ANDYWOLK/freeswitch:feature/FS-11368-use-system-libflite to master

* commit 'bcd355fe':
  FS-11368: [mod_flite] Use system libflite.

FS-11361: [Build-System] Switch Debian packages building script util.sh from jessie stable to stretch stable.

Merge pull request #1553 in FS/freeswitch from ~THEHUNMONKGROUP/freeswitch:feature/FS-11287-provide-option-for-user-managed to master

* commit '96af587b':
  FS-11287: Provide option for user managed streams in Verto

Merge pull request #1548 in FS/freeswitch from ~THEHUNMONKGROUP/freeswitch:bugfix/FS-11284-fix-legacy-broken-video-constraints to master

* commit '31641749':
  FS-11284: Fix legacy/broken video constraints for specifying a video deviceId

Merge pull request #1544 in FS/freeswitch from ~THEHUNMONKGROUP/freeswitch:bugfix/FS-11280-allow-overriding-permissioncallback to master

* commit '36d9f7bc':
  FS-11280: Allow overriding permissionCallback per Verto dialog