.vimrc should not change the screen size

The current version was a relic. When running vim, the editor should just
use the existing screen. Gvim can, of course, set its own screen.

modified:   .vimrc
Make vim and systags use TAGS

All the vim versions around are built with +emacs_tags, so one set of tags
is enough.

modified:   .vimrc
    set tags=./TAGS, etc...
modified:   cmd/systags
    handle either tags or TAGS.
    describe giving CTAGSFLAGS=-e as the way to get TAGS.