Update to 5.1.1

Changelog:
Changes from 5.1 to 5.1.1
-------------------------

5.1.1 is primarily a bug fix release; however, a few minor features were
added.

The ZLE variables YANK_ACTIVE, YANK_START and YANK_END have been added
and are useful for managing highlighting.

The zsh-specific pattern match range tests have been supplemented with
[:INCOMPLETE:] and [:INVALID:] to help detect the state of partially
read multibyte character strings.

(ryoon)