Fixed build after merge from Eridani
Merged revision(s) 30214-30220 from opal/branches/v3_12:
Tidied some random unused variables in VS2010 build files
First cut of Opus audio codec support. Because if it's weirdness there are a number of tweaks required in the stack, e.g. PCM-16 at 12kHz and 24kHz. The really weird part is the RTP/SDP always uses 48kHz stereo regardless of what is actually sent over the wire. In theory, the sample rate and channels can change at any time on a packet by packet basis, but we do not support that. And, interestingly, neither does the standard Xiph library.
Linux build of Opus codec, if loaded into system as package.
Update integer configure tests from PTLib
Fixed issue with make install/uninstall correctly detecting env var build.

Fixed uninstall removing the entire /usr/local/include directory. Less than desirable.
Fixed "internal" opus codec plug in build for *nix.
Added trace logging for if ToNormalisedOptions()/ToCustomisedOptions() function fails to change a media option.
Fixed SIP/SDP fmtp parameter settings for Opus codec.
Fixed build of system based Opus codec library.
Some tidying of Opus plug in (version display, line endings)
Merged revision(s) 30221-30245 from opal/branches/v3_12:
---------------------
r30245
Fixed SDP connect address when NAT is used on incoming call.
---------------------
r30238
Fixed compile of OpenPhone when presence disabled.
---------------------
r30236
Fixed "by inspection" memory leak, pretty sure this never actually happens.
---------------------
r30235
Tidy up of strange log messages when deleting an OPAL transport, to do with closing already closed channels. Benign but confusing.
---------------------
r30234
Extra trace log for sound channel errors.
Fixed SDP connect address when NAT is used on incoming call, extra part for trunk.
Fixed various issues with having mismatch of codec sample rate and RTP timestamps, as done in G.722 and Opus codecs.
Merged revision(s) 30246-30250 from opal/branches/v3_12:
Fixed SDP addresses for RTP session when NAT *not* used, broken in previous fix.
More tweaks with having mismatch of codec sample rate and RTP timestamps, as done in G.722 and Opus codecs.