Local patch revision in PKGREVISION

[Stephen Borrill <netbsd%precedence.co.uk@localhost>]

I sometimes have the need to note that a package has changed due to a 
local patch or an option change. I could just locally bump PKGREVISION, 
but that would be bad. I'd prefer to have a supported suffix to 
PKGREVISION. For example, PKGREVISION= 2p1 would be newer than 2, but 
older than 3.

--
Stephen