Log Message:
Update to 6.72

Upstream changes:
6.72  2018-06-06
  -  Fixed recurrence bug
        The fix in the previous version for a rare recurrence problem broke
        another recurrence form. It is now corrected. Michael Schout (GitHub
        #20)

  -  Fixed version problem
        The wrong version was included in two files for some reason. This is
        fixed.

  -  Documentation fixes
        Fixed a grammatical error reported by Xavier Guimard (GitHub #19).

6.71  2018-06-01
  -  Fixed an extremely rare problem with recurrences
        It is possible to specify a recurrence that never produces a valid
        date. In these cases, looking for dates went into an infinite loop.
        The MaxRecurAttempts config variable was added which will stop that
        from happening. If no occurrence was found, an error condition will
        be set. Dean Hamstead (RT 123708)

  -  Changes file supported
        It was requested that I include a valid Changes file. I wrote a
        simple script to convert the Change6.pod file into a valid Change
        file. The Changes6.pod file is still the canonical source of this
        information! Requested by H. Merijn Brand

  -  Fix for timezone determination
        On MacOS X High Sierra, some of the timezone files were symlinks,
        but not properly followed. This was fixed by Stu Tomlinson (GitHub
        #15).

  -  Time zone fixes
        Newest zoneinfo data (tzdata 2018e)

  -  Documentation fixes
        Minor fix provided by Mohammad S Anwar (GitHub #17)