rc: ignore .pkgsave files

The local parts of rc already skip .sample files; we add .pkgsave to the
list, and add logic for base.

Thanks to @RhodiumToad for getting this started.

Differential Revision: https://reviews.freebsd.org/D27962
Reviewed by: imp
Pull Request: https://github.com/freebsd/freebsd-src/pull/662