[Fedora-packaging] Using %{dist} for conditional compilation

[Roland McGrath]

The cases where conditionals come up in the spec files are for things like
different buildrequires, or different --with/--enable options due to being
able to use system-supplied versions that are compatible on one FC release
and needing to use package-bundled versions on other FC releases.  For lots
of extras packages, the package itself changes much more often than these
differences do, so it really is easier to have a single spec file that uses
conditionals than to maintain branched versions of the spec file.