gitweb: Use print_diff_chunk() for both side-by-side and inline diffs

gitweb: Use print_diff_chunk() for both side-by-side and inline diffs

This renames print_sidebyside_diff_chunk() to print_diff_chunk() and
makes use of it for both side-by-side and inline diffs.  Now diff lines
are always accumulated before they are printed.  This opens the
possibility to preprocess diff output before it's printed, which is
needed for diff refinement highlightning (implemented in incoming
patches).

If print_diff_chunk() was left as is, the new function
print_inline_diff_lines() could reorder diff lines.  It first prints all
context lines, then all removed lines and finally all added lines.  If
the diff output consisted of mixed added and removed lines, gitweb would
reorder these lines.  This is true for combined diff output, for
example:

	 - removed line for first parent
	 + added line for first parent
	  -removed line for second parent
	 ++added line for both parents

would be rendered as:

	- removed line for first parent
	 -removed line for second parent
	+ added line for first parent
	++added line for both parents

To prevent gitweb from reordering lines, print_diff_chunk() calls
print_diff_lines() as soon as it detects that both added and removed
lines are present and there was a class change, and at the end of chunk.

Signed-off-by: Michał Kiedrowicz <michal.kiedrowicz@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>