[merge-tracking] Setting src_rel for WC -> URL copy/move

svn_client__copy_pair_t->src_rel is currently only set for URL -> WC
copy/move operations. I'd like to also set it for WC -> URL ops.
Does this sound reasonable?

I'm currently playing around with this patch:

Index: copy.c
===================================================================
--- copy.c (revision 23396)
+++ copy.c (working copy)
@@ -988,6 +988,10 @@
       svn_client__copy_pair_t *pair = APR_ARRAY_IDX(copy_pairs, i,
                                                     svn_client__copy_pair_t *);
 
+ SVN_ERR(svn_client__path_relative_to_root(&pair->src_rel, pair->src,
+ NULL, ra_session, adm_access,
+ pool));
+
       pair->dst_rel = svn_path_is_child(top_dst_url, pair->dst, pool);
       SVN_ERR(svn_ra_check_path(ra_session,
                                 svn_path_uri_decode(pair->dst_rel, pool),