diff.c

Shelving: implement 'svn diff' on shelves.

'svn diff --cl=svn:shelf:SHELF' runs a diff on the shelf named SHELF. This
is an alternative to the 'svn shelf-diff' command. Most 'svn diff' options
are supported; --depth and --ignore-ancestry are not yet supported.

* subversion/include/private/svn_client_private.h,
subversion/libsvn_client/shelf.c
(svn_client__shelf_diff): Add depth and ignore-ancestry options (not yet
supported). Constify the diff processor parameter.
(file_changed, file_deleted, file_added, diff_baton_t): Adjust for that
'const' change.

* subversion/libsvn_client/diff.c
(diff_shelf, diff_shelves): New.
(do_diff): Look for shelf diffs in the WC-WC diff case.