In the post commit handling: use a smarter sqlite query to avoid a coded
recursion over all descendants in c code.

When I originally wrote this code, we couldn't assume a single-db yet,
but now we can rely on an index-backed sqlite query.

* subversion/libsvn_wc/wc-queries.sql
  (STMT_COMMIT_DESCENDANT_TO_BASE): Make query recursive as...
  (STMT_COMMIT_DESCENDANTS_TO_BASE): ... this.

* subversion/libsvn_wc/wc_db.c
  (moved_descendant_commit): Update comment.
  (descendant_commit): Update comment. Replace implementation with smarter
     query.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1443989 13f79535-47bb-0310-9956-ffa450edef68