Enhancements to trace logging, include threads and context ID.
Changed default opal_conf.xml to allow more than just G.711 uLaw and not to clutter log file with debug logs.
Added to opal_conf.xml item for "disable-transcoding".
Updated build/buildopal.sh to use correct ./configure items for PTLib, allow for something other than standard install directory for PTLib/OPAL and be able to easily bind to a specific release of PTLib/OPAL.
These codecs are non-free which creates issues for distributions, so
let's not require these by default to run our example configs. We can
add back in iLBC once we resolve the licensing situation with our
in-tree implementation.