cygport: allow setting prev:, curr:, and test: in autogenerated setup.hint

[Andrew Schulman]

> It seems you've re-invented something that David Rothenberger has
> implemented before in a slightly different way:
> 
> http://thread.gmane.org/gmane.os.cygwin.applications/26034
> 
> It's also integrated in my patched-up version of cygport here:
> 
> git://repo.or.cz/cygport/rpm-style.git
> 
> FWIW, I've been using Dave's patch a few times and it seems slightly
> less verbose than what you've got.

OK.  Sure, VERSIONS="curr:1.7.3.0-2 test:2.0.0-b8-1" also works, and it has the
advantage of not baking in the current 3-version prev/curr/test setup quite so
much. OTOH setting PREV, CURR and TEST feels a little more natural to me with
the current 3-version setup.

Either way would be fine with me, as long as I have a way of automatically
setting the versions in the cygport file, instead of having to manually edit
setup.hint after the build.

Andrew