Fix: Missing 'null' patterns handler

Zepto and Standalone versions breaks due to lack of treatment when dealing with
elements with pattern attribute undefined. jQuery was gently bypassing this
failure but, the other libraries are blaming my fault.

From now on, Parsley will automatically add pattern attribute validation when
two requirements are satisfied:
1. Pattern attribute IS string. This excludes undefined on old browsers and
also, on new HTML5 compliant browsers, ignores cases which the attribute is not
defined.
2. Pattern attribute HAS length. An empty pattern doesn't make sense and also
won't never be valid. If, for some unknown bizarre cause, we need an empty
field, pattern="^$" should do the trick

At this time, jQuery and Zepto tests should happly passes.
Minified version for pattern attribute support

With the directions[1] given by @guillaumepotier, this commit brings the
minified version under the name of 1.1.11-dev

[1] https://github.com/guillaumepotier/Parsley.js/pull/128#issuecomment-13609870