This was momentarily called force_send_silence_when_idle, but that was
non-obvious as you had to set that value to true to be able to not
send silence when idle.  This name describes the purpose much better.

We were handling the "send silence but not comfort noise" case in both
silence_stream_file_read and switch_generate_sln_silence.  This
changes the former to rely on the latter.

If set to true, this prevents us from overriding the value of
send_silence_when_idle.  When that is unset or set to zero and SRTP is
engaged, we typically override the value because many devices can't
handle gaps in the SRTP stream.

This variable is mostly for testing whether particular devices can
handle this behavior.  Use at your own risk.

In commit 55d01d3d we set
send_silence_when_idle to -1 rather than 400 when SRTP is engaged.
But this left no way to enable white noise silence when desired.

When SRTP is engaged we can't simply not send RTP because it breaks
too many devices.  So we need to prevent send_silence_when_idle from
being unset or being set to zero.  This change allows it to be set to
other values so as to feed white noise rather than all zeros into the
codec.

When the channel variable send_silence_when_idle was set to zero,
switch_ivr_sleep was calling SWITCH_IVR_VERIFY_SILENCE_DIVISOR on it
anyway, causing it to be set to 400.  The only way to get the behavior
of not sending silence when idle was to unset the variable completely.

This corrects the behavior such that setting the value to zero has the
same effect as leaving it unset.

In UNIX, text files by definition end with a newline.

write(3) can write fewer bytes than was requested for any number of
reasons.  The correct behavior is to retry unless there is an error.

If there is an error, try to unlink the file; no sense in leaving
corrupted data laying around.

The default value of libdir is (unexpanded) '${exec_prefix}/lib'.  In
the non-FHS path this is fine because it only ends up in a variable
where it will be expanded later.  By using this to define modulesdir
we let it slip into a define where it made no sense.

This avoids searching the string repeatedly with strchr.

We were incorrectly parsing usernames and domains starting with "sip"
if there was no sip: or sips: scheme in the string.

We were also incorrectly parsing usernames containing a colon even if
a scheme was given.

This also refactors the function for hopefully greater clarity.

In commit 7efeabbd Anthony fixed the
handling of sip:example.com and sips:example.com URLs, however he
introduced a regression causing URLs starting with 's' to be parsed
incorrectly.

In commit 7d2456ea Brian fixed the
regression, but introduced a regression causing sips:example.com URLs
to be handled incorrectly.

Order the default configure flags in the order they show up in
configure --help, and order our own alphabetically.

When --enable-fhs is passed to configure, we set all paths by default
in a way compliant with FHS, the Filesystem Hierarchy Standard.

  http://www.pathname.com/fhs/

Each path may still be overridden by passing the specific flag for it.

This previous change fixes the issue on 64bit but if trying to compile a 32bit build you end up breaking the types on 32bit.

Commandline Fu for dumping the various defines for gcc are as follows:

gcc -m64 -dM -E - <<<''

gcc -m32 -dM -E - <<<''

FS-6226Prevent DTMF from traversing bridged channels, but still allow me to send DTMF via API or dp app (uuid_send_dtmf or send_dtmf)

Originally we did the same thing with SRTP that we do without SRTP,
which is to simply not send packets when e.g. sleep is called.

At commits d6332397 and
5259814a we enabled sending silence
packets with comfort noise when SRTP is active.  We appear to have
done this for interop purposes; many devices can't handle gaps in the
stream of SRTP packets.

But our current comfort noise implementation doesn't take the codec
rate into account (FS-6291), so on 16kHz codecs the constant we chose
created an annoying level of static between sound file playback.

With this commit we preserve the sending of SRTP packets during idle
periods, but make those packets completely silent.

Thanks-to: Anthony Minessale <anthm@freeswitch.org>

FS-5053 --resolve