Document process for rebuilding pgsql library on Mac packaging machines

The pgsql library on the Mac packaging machine is a copy of the same library taken from the old build machine. This is due to previous release managers not documenting how to rebuild the library.

The process for acquiriing fresh pgsql source and rebuilding it for Mac should be rediscovered and documented in the Release Engineering wiki page on preparing package build machines – http://wikis.in.nokia.com/QtSoftware/QtRelEngPackageMachineSetup.

The desirability of updating to the latest pgsql version should also be evaluated.