[1.5.x] Fixed #18210 -- Escaped special characters in reverse prefixes.

      Ensured that special characters passed in to reverse via the
prefix argument are properly escaped so that calls to
django.utils.regex_helpers.normalize and/or string formatting
operations don't result in exceptions.

Thanks to toofishes for the error report.

Backport of 90e530978d590a5bdcf75525aa03f844766018b8 from master.