Add flavor support to routines that convert port origins to shell variable
names. The character '@' is illegal in such names and must be converted to
a legal character same as [-+./].
remobve post processing of "pkg check -dn" output, which was a left-over
from pre-PKG_NG times.

Reported by: koobs (invalid @), tatsuki_makino@hotmail.com (pkg check)
Approved by: antoine (implicit)