Rename lock to willNavigate

The phantomjs documentation[1] indicates that the lock variable is
named 'willNavigate'. After a quick test, the values passed reflect that
name, true indicating navigation will happen, false indicating it will
not.

[1]:
https://github.com/ariya/phantomjs/wiki/API-Reference-WebPage#onnavigationrequested
Update currentResponse on Navigation

Previously, when clicking on a link in a page or submitting a form,
Casper.page would be updated to reflect the newly loaded page, but
Casper.currentResponse would not.  This caused the response passed to
'then' callbacks to only reflect the initial page load.  This patch
resolves that issue so that Casper's page and currentResponse are
consistent and subsequent 'then' call backs receive the response of the
most recent main page load.
jshint flags
style fixes
Merge pull request #460 from zeroem/update-request-url

Make Casper.currentResponse consistent with Casper.page