Revert.  This is a mistake.

  The idea of variables containing either strings or vectors/arrays
 is a good one, but this implementation is problematic because
 we can't differentiate things clearly.

  Consider the case of:

        maildir_prefix( { "foo", "bar", "baz" } );

  This is setting the value of the variable 'maildir_prefix' to an
 array.  Well and good.

  Now consider retrieving the value:

        x = maildir_prefix()

  You can't tell which value-type to return ("table" v.s. "string")
 short of looking up both and returning the first non-empty one.

  What you should be able to do is say "Return the value .. in table
 form", but you can only detect the expectation by seeing
"lua_istable(L,-1)" - which isnt' set on the accessor-case.

  Updates #202.

  For the moment we'll sidestep the issue :

        maildir_prefix( "/path/to/maildir|/path/to/maildir2|..." );

  That is ugly, but will be consistent, easy to debug, and tolerable.