Avoid trimming the line at the point.

Some new fancy stuff I'm adding results in the line at the point being queued
for whitespace trimming, but it actually contains useful whitespace, so we
don't want to trim it.
Revamp electric brace handling.

I don't always want blocks to be multiline, but I do like my braces to be
matched. So now I match the braces, and if I press ENTER while betwixt an
open/close brace pair, then I do the block expansion. More DWIM!