added new target "onepcm" that will build the single pcm and run make to
get the dict build into libCore. Support out of source build and get rid
of second makeonepch.sh that is now part of makeonepcm.sh.


git-svn-id: https://root.cern.ch/svn/root/trunk@48642 27541ba8-7e3a-0410-8455-c3a389f83636