Revision 1913219

Revise pool usage for .get_rev_prop() to the standard "scratch_pool"
pattern, rather than using a stored pool.

* tools/hook-scripts/mailer/mailer.py:
  (Commit.__init__): pass POOL for the .get_rev_prop() call
  (PropChange.generate): use self.pool (from OutputBase) as the
    scratch pool for .get_rev_prop()
  (generate_content): pass POOL for the .get_rev_prop() call
  (DiffGenerator.__getitem__): use our stored pool as the scratch pool
    for the .get_rev_prop() call.
  (Repository.__init__): rename instance variable to HOLD_POOL to
    indicate its use for holding values (FS roots). Update call to
    .get_rev_prop()
  (Repository.get_rev_prop): take a SCRATCH_POOL argument, and use
    that pool rather than the pool stored in the instance.
  (Repository.get_root): track change to self.HOLD_POOL