I know that the error for php-5.4 incompatibility confusingly says
that squirrelmail is incompatible with php-5 entirely, but it is just
php-5.4 that it is incompatible with. I'm adding some more verbose and
setting the default to 5.3 if php isn't installed, but there's not a
lot else I can do.
There is an open PR to make the error message more clear, but at the end
of the day php-5.4 compatibility is waiting only on the SM team to
make another release.
Feature safe: yes