gitweb: Better cutting matched string and its context

gitweb: Better cutting matched string and its context

Improve look of commit search output ('search' view) by better cutting
of matched string and its context in match info, as suggested by Junio.
For example, if you are looking for "very long search string" in the
following line:

    Could somebody test this with very long search string, and see how

you would now see:

    ...this with <<very long ... string>>, and see...

instead of:

    Could som... <<very long search...>>, and see...

(where <<something>> denotes emphasized / colored fragment; matched
fragment to be more exact).

For this feature, support for fourth [optional] parameter to chop_str
subroutine was added.  This fourth parameter is used to denote where
to cut string to make it shorter.  chop_str can now cut at the
beginning (from the _left_ side of the string), in the middle
(_center_ of the string), or at the end (from the _right_ side of
the string); cutting from right is the default:

  chop_str(somestring, len, slop, 'left')    ->  ' ...string'
  chop_str(somestring, len, slop, 'center')  ->  'som ... ing'
  chop_str(somestring, len, slop, 'right')   ->  'somestr... '

If you want to use default slop (default additional length), use undef
as value for third parameter to chop_str.

While at it, return from chop_str early if given string is so short
that chop_str couldn't shorten it.  Simplify also regexp used by
chop_str.  Make ellipsis (dots) stick to shortened fragment for
cutting at ends, to better see which part got shortened.

Simplify passing all arguments to chop_str in chop_and_escape_str
subroutine. This was needed to pass additional options to chop_str.

Signed-off-by: Jakub Narebski <redacted>
Signed-off-by: Junio C Hamano <redacted>