Lua: add Variable:totab()

In favor of establishing symmetry with :fromtab
lua: add rtt_rospack based find_rospack
add basic rttlib.help
optimize rtt_rospack_find + fix to work with services
Merge branch 'master' of git://gitorious.org/orocos-toolchain/ocl-mk into toolchain-2.7
Merge branch 'master' into toolchain-2.7