Use omalloc for new/delete (due to Hans)

NOTE: only for resulting Singular executable (not for any of our libs)
Further compiler flags tweaking
Further template instantiation

NOTE: still not working withou implicit template instantiation (due to some undefined std::__* functions related to sorting...)
Fixed Adi's '#ifdef HAVE_RINGS || HAVE_RINGS_LOC'
Fixed the generation of "desktop/Singular*.desktop" on FreeBSD with non-gnu make