GHC versions are now of the form AA.BB.C, where AA is the major
version, BB is the minor version, and C is the patchlevel.

Part of this commit accidentally ended up in an earlier commit to
fptools/ghc/mk/version.mk, which contains some comments on the version
rationale.  Excerpt:

# ProjectVersionInt does *not* contain the patchlevel (rationale: this
# figure is used for conditional compilations, and library interfaces
# etc. are not supposed to change between patchlevels).

i.e. a patchlevel is for bugfixes only, no new features or
interface-changing changes.  Unfortunately, we made this mistake in
4.04pl1, and won't be making it again.