color-words: enable REG_NEWLINE to help user

color-words: enable REG_NEWLINE to help user

We silently truncate a match at the newline, which may lead to
unexpected behaviour, e.g., when matching "<[^>]*>" against

  <foo
  bar>

since then "<foo" becomes a word (and "bar>" doesn't!) even though the
regex said only angle-bracket-delimited things can be words.

To alleviate the problem slightly, use REG_NEWLINE so that negated
classes can't match a newline.  Of course newlines can still be
matched explicitly.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>