Packages: change url for xercesc
build: respect --no-ccache
BinaryDist: check for pbzip2
libnabo: force use of BB boost, avoid system
libpointmatcher: disable fopenmp for Darwin, fix boost
build.py: Clarification for ccache
Do not disable openmp on darwin yet, needs to be done for 10.8 only
Make libpointmatcher boost fix work for Mac as well