Interactions between quote matching and completions.

When tab-enter completing HTML attributes, as an example, if the completion includes a trailing quote the current behaviour of pressing tab to escape works, but additionally, hitting a matching quote should also bump you outside.  Currently it just adds another double quote and makes the syntax highlighting on the rest of the file go all funky.

Tried making a video, ended up green.  Hate when that happens.  (Silly old cinema displays not supporting HDCP!)