Open delta source and target streams lazily in the Ev2 edit receiver.
Open delta source and target streams lazily in the Ev2 edit receiver.

Previously, when driving an Ev2 status editor through the Ev1->Ev2 adapter,
an empty temporary file would be created for every file mentioned in the
status report, even though a status edit drive does not transmit any text
deltas.

* subversion/libsvn_delta/compat.c
  (open_delta_base, open_delta_target): Lazy-open stream handlers for opening
   the delta source and target files.
  (ev2_apply_textdelta): Open the delta source and target lazily.
   Remove the now-unused local variable 'scratch_pool'.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@1576277 13f79535-47bb-0310-9956-ffa450edef68

YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion