Mk/bsd.sanity.mk: Flag non-integer PORTREVISION/PORTEPOCH

Currently they are not checked and something like PORTREVISION=foo
or just PORTREVISION= is accepted. Some ports use indirection via
custom variables for them so it is worthwhile to check that they
are set to sane values.

While here fix ports that currently have non-integer PORTREVISION
or PORTEPOCH.

Approved by: portmgr (mat)
Differential Revision: https://reviews.freebsd.org/D21225