More reliably push auto-complete to the start of 'completion-at-point-functions

Without this, add-to-list would not move auto-complete ahead of any
functions listed before it.
Provide option to force use of default font for symbols

On my Mac, this seems to be necessary, otherwise Emacs always picks a
different font for symbols. That font inevitably has a different width,
so the resulting rendering is ugly.
Make ac-slime work with TAB in the slime REPL
Drop pointback (see #133)
Don't show trailing whitespace in twittering-mode, if installed