vim mappings, default to tabs, and no gitprompt <>

added an alias to make vim default to tabs when multiple filnames are
specified, removed a pair of mappings that a) weren't effective, and b)
overwrote a useful mapping, added mappings for '/' and '?' that jump to the
command window for each, and removed an env variable in bashrc that added an
annoying '<>' to the git prompt (something about comparing to upstream, but
didn't seem to work?)