2015-12-01  Alex Dunn  <dunn.alex@gmail.com>

        Improve version-to-list parsing

        * lisp/subr.el (version-regexp-alist): allow "." as priority separator
        * lisp/subr.el (version-to-list): more helpful error messages
        * lisp/subr.el (version-to-list): ".5" is valid (update docstring)
        * lisp/subr.el (version-to-list): make "22.8X3" invalid
        * test/lisp/subr-tests.el (ert-test-version-parsing): parsing tests