Add CXX variable to Makefile. Add separate PROJ_ sections for C++ as well as
pcap, so John does not fail building even if they do. Also add uaf2john and
truecrypt_volume2john to the main targets and move office2john to unused.

PROJ_CXX and PROJ_PCAP is only added to Linux, BSD and Windows for now.
Bugfix in keystore2john.