Merge pull request #28 from smuzaffar/master

big objs symlink fixed; properly set CLASS variables for various products
Merge pull request #29 from smuzaffar/master

do not generate lcg/root dict if all files are skipped
Merge pull request #30 from smuzaffar/master

dxr rules added; cleanup of various flags for osx/linux
drop LD_UNIT flags defaults, these should be provided via cxxcompiler
Do not pass --exclude-libs on Darwin/OSX

The option, --exclude-libs, is not supported by cctools Darwin linker.

Signed-off-by: David Abdurachmanov <davidlt@cern.ch>
various osx fixes: fixed big plugin extension; do not pass -L for non existsing project directories to link command