Add the dav-mirror-autocheck.sh regression tests promised in r1936010-r1936031.

The mirror harness now runs everything against URI-encoded master and
slave locations ("master loc"/"slave loc", deliberately of different
lengths) and a slash-terminated SVNMasterURI, exercising the encoding
fixes.
New coverage:
- Log messages and revision properties containing the slave URL
  round-trip verbatim (create-txn-with-props POST bodies).
- The full lock lifecycle (a URL-bearing lock comment stored on the
  master, locked commit, release-on-commit, and explicit UNLOCK)
- Raw HTTP reads of open-transaction resources through the slave
  (file content verbatim, PROPFIND hrefs translated, XML-mime-typed
  content guarded).
- The one remaining SVN-3445 residual: dead-property values rewritten
  in a proxied multistatus, reported as XFAIL

The last 2 tests require curl for the transaction probes, no svn client
can hold a transaction open or address !svn/txr URIs

* subversion/tests/cmdline/dav-mirror-autocheck.sh: As above and fix a
  stray ">" in the generated master vhost's ServerName.
* subversion/mod_dav_svn/mirror.c
  (proxy_request_fixup_destination, response_is_xml): Correct some stale
  comments

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/proxy-move-copy-fix@1936032 13f79535-47bb-0310-9956-ffa450edef68