Building feh without PREFIX=... leads to errors about missing fonts,
since the builtin font paths are hardcoded relative to the PREFIX.
The prefix must be supplied during build, and perhaps during install
(which must be done separately since there is no build dependency on
installation).
Signed-off-by: Jack Nagel <jacknagel@gmail.com>
Made the formula less likely to break on upgrades by replacing the patch
by environment variables set on install.
Also removed the dependency on libpng.
ClosesHomebrew/homebrew#4221.
Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>
