Revision 1834787

Correct the use of backslash-space sequence in Python strings.

Python docs state: "Changed in version 3.6: Unrecognized escape sequences
produce a DeprecationWarning. In some future version of Python they will be
a SyntaxError."

Where meant to be a literal string, replace with backslash-backslash-space;
where meant to be a regex, remove the backslash as it is unnecessary in
ordinary regular expressions.

Suggested by: danielsh

* subversion/tests/cmdline/externals_tests.py
  Double the backslashes in externals definitions.

* subversion/tests/cmdline/diff_tests.py
* subversion/tests/cmdline/log_tests.py
* subversion/tests/cmdline/patch_tests.py
* subversion/tests/cmdline/special_tests.py
  Double the backslashes in "\ No newline at end of..." diff lines.

* subversion/tests/cmdline/svnadmin_tests.py
  (dump_exclude_all_rev_changes): Remove unnecessary escapes in regexes.