incr revision / portindex

[Daniel J. Luke]

Hi macports-dev,

Looks like the change in 10aaad9b10e7350e76676ebdb5acfc950b800273 caused behavior I didn't expect on my Monterey system. Since I'm using a git checkout for my portfiles on that host and I was running darwin 20 when I did `port sync` after that change hit, my portindex had, for example 1.5.0_1 for zstd. After upgrading to Monterey, that means 'port outdated' thinks zstd is outdated, but trying to install it installs 1.5.0_0. (so `port outdated` still thinks it's outdated).

Easy fix for me is to blow out my PortIndex and create a new one - but this is the first time I think I've ever had to do that when upgrading macOS.

I'd suggest that we should avoid having platform (or variant) blocks change any of epoc,version,revision even in a case like this (when presumably that was done to avoid unnecessary rebuilds for some people).

In any event - I thought I'd post, if for no other reason than to save someone some time if they also see this behavior. 
-- 
Daniel J. Luke