Fix bug reported by Roger Peppe, namely that

	regexec(regcomp("^good"), "hello\ngoodbye", nil, 0) == 0

The code to skip forward line by line when matching
a pattern beginning with ^ was off by one in regexec.c.

I changed rregexec.c to use the new(er than libregexp)
runestrchr function so that it looks more like regexec.