Make sure plugins use the same php version as the main squirrelmail
port. This is an issue for packages, where dependencies are computed
before other dependencies are installed.
While we're at it, remove the vestigial WITHOUT_WWWDIR thing. I'm
just assuming noone uses it, and if you do, then you can set
SQUIRRELDIR= as noted in the file---this is the same setting used in
the main squirrelmail port.
Feature safe: yes