allow "exit search and move to current match" when no more matches are found

[jonvuri]

Copying from t9md#12 made by @slippycheeze. I'll try to address this shortly with a new option.

I know it seems odd, but sometimes the behaviour I desire from search is:

• invoke search
• type "foo", bringing me to a match
• type "z", no match
• hit enter, desiring to terminate search at "foo" as last matched
  That's usually triggered when I'm searching for something like "adding hosts", and it turns out the correct text was "added hosts", but I get the extra text typed out before my brain catches up with the fact that I'm looking at the correct line.

This is identical to the behaviour of Emacs in this situation, and fits nicely with backspace to remove characters and correct the match...