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.