allow uppercase http methods

Both the HTTP 1.1 spec ([5.1.1 Method](http://www.ietf.org/rfc/rfc2616.txt)) and PhantomJS [webpage.cpp](https://github.com/ariya/phantomjs/blob/master/src/webpage.cpp#L811) require or support uppercase HTTP Methods.

This patch adds that functionality to CasperJS.

I wasn't sure how you wanted tests like this structured. I ran all tests locally and they pass on top of PhantomJS 1.9.0.