PHP/HHVM builds now execute additional custom compile step

Change effective on 13 January 2015

During a build, a composer compile command, if defined in composer.json, will now be executed after dependencies have been installed. This may be used to perform certain long-running warmup or compilation steps that should not be part of a regular Composer post-install-cmd step. Please refer to the Build Behavior section of the PHP reference documentation for details.