shell-common: remove redundant functions

core-functions.sh already has these.  They should've been deleted when
they were moved there.
Tease apart non-interactive vs. interactive setup.

In some environments, there were issues with virtualenvwrapper being
setup and the LESSOPEN feature.  This moves the virtualenvwrapper setup
to be in interactive.sh, and the basics are now being done in
noninteractive.sh.  Hopefully, this will help maintain a better
separation.
gitconfig: remove the extra, unnecessary quoting around set-origin
user/jszakmeister: try colorizing less for man pages

This is experimental, but using Vim for man pages is taking a bit too
long on my older machine.  This seems like a good compromise.