make sure cas url is parsed properly

At some point, it seems parseUrl changed its behavior
so that it always returns a full object.  that means
my 'urlp.host === undefined' condition fails, because
the 'host' key *is* defined, just its value is null.

So slot in another condition, that if the value is falsy,
return is urlp.href

Made a test that passes whether CAS_HOST is http, https, or
neither.

closes #7

modified:   lib/cas_validate.js

new file:   test/loadup_tests.js