Revert to correct version scheme

Radiant version scheme shifts RADIANT_MAJOR and RADIANT_MINOR one position to the right, as in RADIANT_MAJOR to be what we would call "minor" and RADIANT_MINOR "patch". See for instance the preferences folder created in ~/.netradiant on Linux, that's 1.1.5 when it should be 1.5.0. The original Makefile clearly sets those values following the scheme above, same for gtkradiant.