Port r1631115 and -71 from FSFS to BDB.

* subversion/libsvn_fs_base/bdb/changes-table.c
  (change_to_fs_change): New struct copy / conversion utility.
  (fold_change): Use the new utility to create new hash entries,
                 remember deletions being replaced by additions
                 and revert to them upon deletion again.
  (svn_fs_bdb__changes_fetch): Rename subpool to iterpool and use a new
                               subpool for the temporary deletions hash.

* subversion/tests/libsvn_fs/fs-test.c
  (test_delete_replaced_paths_changed): Test now works on BDB as well.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1631176 13f79535-47bb-0310-9956-ffa450edef68