Fix issue #4538 "'load' strips r1 references in mergeinfo": don't filter out
references to r1 in mergeinfo during 'svnadmin load' and 'svnrdump load'.

r1 is not an invalid mergeinfo source revision, merely an unlikely one, and
we don't treat it as invalid anywhere else.

This reverts r941438 which has been in place since v1.7.0. Note also that
this commit didn't remove r0 mergeinfo, only r1, despite the claim in its
log message.

* subversion/libsvn_repos/load-fs-vtable.c,
  subversion/svnrdump/load_editor.c
  (renumber_mergeinfo_revs): Don't filter out references to r1.
    Canonicalize mergeinfo, where previously the combination of sorting
    followed by filtering achieved canonicalization.

* subversion/svndumpfilter/svndumpfilter.c
  (adjust_mergeinfo): Remove a comment that said r1 is invalid.

* subversion/tests/cmdline/svndumpfilter_tests.py
  (filter_mergeinfo_revs_outside_of_dump_stream): Correct a comment that
    said r1 is invalid, written in r941408.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1646505 13f79535-47bb-0310-9956-ffa450edef68