Sane ctags support in vim; disable insane "features"

* CDPATH in a shell is fine until you can no longer sanely tab-complete
  into folders because the shell tries to shove folders from other
  locations into your autocomplete.
* Highlighting HTML/SQL in PHP strings is fine until it gets too
  brainfucked because strings don't look like strings anymore.

Vim now recursively searches for the tags file, which allows for opening
code from within the project tree (and not only from its root, or
wherever one puts the tags file).

Disable autofold for git commit message editing in vim. Submitting
.vimrc with 'git commit -v' has always been a little pain in the neck.