Clarify some pool usage by tweaking doc strings and renaming pool
parameters.

* subversion/include/private/svn_mergeinfo_private.h
  (svn_mergeinfo__remove_empty_rangelists): Rename the pool parameter to
    'scratch_pool' and remove the (too-specific) mention of it from the doc
    string since it's now obvious.

* subversion/include/svn_mergeinfo.h
  (svn_mergeinfo_parse): Document that the result is allocated deeply in the
    pool, since it is and apparently always has been.

* subversion/libsvn_client/mergeinfo.h
  (svn_client__parse_mergeinfo): Same.

* subversion/libsvn_subr/mergeinfo.c
  (parse_revision_line, parse_top): Document the basic purpose and the pool
    usage.
  (svn_mergeinfo__remove_empty_rangelists): Rename the pool parameter as
    mentioned above.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1569803 13f79535-47bb-0310-9956-ffa450edef68
In libsvn_client diff handling, move the creation of diff processors up
the callchain to allow reusing more code code between diff and diff
summarize.

* subversion/libsvn_client/diff.c
  (diff_wc_wc): Allow passing NULL for callback_baton. No functional
    changes.
  (diff_repos_wc): Add argument to allow disabling a tree wrapping.
    Allow a NULL callback baton, and always initialize the urls in the baton.

  (do_diff): Update arguments to accept a diff processor instead of callbacks.

  (diff_summarize_repos_wc,
   diff_summarize_wc_wc): Remove now unused functions.

  (do_diff_summarize): Construct diff processor and pass it to the common
    diff functions.

  (svn_client_diff6,
   svn_client_diff_peg6): Wrap callbacks to update call of do_diff.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1569804 13f79535-47bb-0310-9956-ffa450edef68