gitweb: Add combined diff support to git_patchset_body

gitweb: Add combined diff support to git_patchset_body

Calling convention for combined diff similar to the one for
git_difftree_body subroutine: difftree info (first parameter) must be
result of calling git-diff-tree with -c/--cc option, and all parents
of a commit must be passed as last parameters. See also description in
  "gitweb: Add combined diff support to git_difftree_body"

This ability is not used yet.

Generating "src" file name for renames in combined diff was separated
into fill_from_file_info subroutine; git_difftree_body was modified to
use it. Currently git_difftree_body and git_patchset_body fills this
info separately.

The from-file line in two-line from-file/to-file header is not
hyperlinked: there can be more than one "from"/"src" file. This
differs from HTML output of ordinary (not combined) diff.

format_diff_line subroutine needs extra $from/$to parameters to format
combined diff patch line correctly.

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