Pre-commit script to reject commits

[markd at macports.org]

>> Thanks for the clarification, I think you are kind of right. But it
>> will
>> always hit someone not affected by the update. For example, changing
>> depends_* inside some variants and incrementing the revsion forces all
>> users to recompile - even if they don't use this variant...
>
>And yet, incrementing the revision is the correct thing to do, if
>doing so will fix the install for even just a few users, even at the
>risk of unnecessarily rebuilding the port for others. For example,
>perl5.8 was updated from revision 1 to 2 in r34508. As I understand
>it, the change was irrelevant for those using gcc 4.0 (i.e. at least
>all Mac users), but was necessary for those using gcc 4.2 (perhaps
>Linux or FreeBSD users). Oh well.

I don't think we're all have the same understanding of when the port
revision number should be incremented.  If there are guidelines we could
all agree to it could be documented, and (along with  some nagging) we'd
probably see a lot less variance, not that automation wouldn't be fine too.

Mark