Don't capture control-tab events

This allows control-tabbing out of the tab where you're editing a paste. It also includes a small amount of code cleanup.

I started writing a "shift-tab deindents a line" feature but it turns out to have some complicating factors:

* if you shift-tab a line that's like `<whitespace>text<whitespace>` should it deindent the first whitespace or the second?
* if you shift-tab a multi-line selection it should deindent each line, but shouldn't mess up lines that're already at tab-stop 0
* cross-browser excitement

So I bailed.