ENH: determine the current system also in cpack, so the search paths are
loaded
Additionally the makefile in cmCPackGenericGenerator is now protected
instead of private, so with these two changes the cpack generators should
now be able to find their tools and how to call these tools from cmake
scripts, instead of hardcoding the search order and command line (as done
e.g. in cmCPackZIPGenerator.cxx)

Alex