Remember watir elements until the page changes rather than allocated a new wrapped object each time the element is accessed.
Allow caching to be disabled for individual elements, and add the default caching setting to the configuration.
Add support for validator blocks by defining +add_validator+.
Add a validator block to test_github to test support for it.
Check to ensure that a page's entry_url actually exists, rather than silently continue on the wrong page.
Merge branch 'cached-elems'

 * Remember watir elements until the page changes rather than allocated a new
   wrapped object each time the element is accessed.
 * Allow caching to be disabled for individual elements, and add the default
   caching setting to the configuration.
Add documentation for +:cache+ to +element+.
Remove accidental duplicate line in definition of wrap_watir.initialize.