'version.h: version' from 697d818 does nothing, and makes version.h
a makefile item (it is not meant to be). Build failure, if 'version'
is not listed in 'all:'
'version.cpp: version' makes the 'version' function a prerequisite
for obj/version.o, which is all that's needed.
'-f' added to 'rm version.h'. Fixes make clean error.
Merge pull request #857 from atomicdryad/makefile_drama_oh_my

'version.h: version' => 'version.cpp: version'