Change function order. No functional change.

* subversion/libsvn_fs_x/transaction.c
  (store_l2p_index_entry,
   store_p2l_index_entry,
   allocate_item_index): Move up.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1568799 13f79535-47bb-0310-9956-ffa450edef68