gitweb: Support comparing blobs (files) with different names
Fix the bug that caused "blobdiff" view called with new style URI for a rename with change diff to be show as new (added) file diff.
New style URI for "blobdiff" for rename means with $hash_base ('hb') and $hash_parent_base ('hpb') paramaters denoting tree-ish (usually commit) of a blobs being compared, together with both $file_name ('f') and $file_parent ('fp') parameters.
It is done by adding $file_parent ('fp') to the path limiter, meaning that diff command becomes:
git diff-tree [options] hpb hb -- fp f
Other option would be finding hash of a blob using git_get_hash_by_path subroutine and comparing blobs using git-diff, or using extended SHA-1 syntax and compare blobs using git-diff:
git diff [options] hpb:fp hp:f
Signed-off-by: Jakub Narebski <email@example.com> Signed-off-by: Junio C Hamano <firstname.lastname@example.org>