On the log-addressing branch:  Minor pool usage optimization.

* subversion/libsvn_fs_fs/transaction.c
  (upgrade_transaction): iterpool can be used as scratch_pool

Suggested by: philip

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/log-addressing@1535715 13f79535-47bb-0310-9956-ffa450edef68