Don't overwritten ac-triggered value(#286)

`ac-triggered` value should not be overwritten with `t` if its previous
value is `'command`.
Merge pull request #320 from auto-complete/not-stop-dictionary-word

Don't overwritten ac-triggered value(#286)
added tcl-mode to custom ac-modes
Merge pull request #322 from vogdan/patch-1

added tcl-mode to custom ac-modes