On the fsfs-format7 branch:  Replicate the FS commit API change
from FSFS in FSX.

* subversion/libsvn_fs_x/tree.h
  (svn_fs_x__commit_txn): add set_timestamp parameter

* subversion/libsvn_fs_x/transaction.h
  (svn_fs_x__commit): ditto

* subversion/libsvn_fs_x/tree.c
  (svn_fs_x__commit_txn): pass through

* subversion/libsvn_fs_x/transaction.c
  (commit_baton): add set_timestamp member
  (commit_body): set svn:date TXN property only if set_timestamp is true
  (svn_fs_x__commit): pass through via baton 


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsfs-format7@1507265 13f79535-47bb-0310-9956-ffa450edef68