Send-on-enter and autocomplete both listen for "return" keypresses, and could race. Have autocomplete let other handlers take a shot at the action before it does.

Also, fix a case where ":)" and the suffix list (which lets you type someone is 100% to blame here (@epriestley) and get the results you want) interacted badly, so ":)" cancels the autocompleter like ":3" does.

• Typed "@xxx" and mashed return real fast over and over again while reloading the page. Before: sometimes handlers raced and text submitted. After: always handled by autocomplete behavior.
• Typed ":", ")", "<return>", sent an emoticon (previously: no).