Fix #158: carp when drag is invoked on WebElement

Drag is no longer in the JSONWireProtocol for web elements. It doesn't
work with HTML5 elements in Webdriver, not on the binding
side. References:

https://code.google.com/p/selenium/issues/detail?id=6315
http://elementalselenium.com/tips/39-drag-and-drop
https://gist.github.com/rcorreia/2362544
Remove eval around drag test in 02-webelement.t

for #158: Drag no longer blows up the test now that it's carping instead
of invoking an invalid endpoint.
Merge pull request #163 from gempesaw/deprecate-drag

Drag is no longer in the JSONWireProtocol and should be deprecated.