(bug 35658) make mw.Uri handle uris w/o protocol or host

(bug 35658) make mw.Uri handle uris w/o protocol or host

Includes testcase.

mw.Uri already supplied the protocol if it was missing and
document.location was set. Newly it also supplies the host (and port)
from document.location if that is set. That enables handling of
root-relative URls like "/some/path".

Changeset 2/3: rename test file from mediaWiki.Uri.test.js to
mediawiki.Uri.test.js.

Changeset 4: fix jasmine tests. Test for 'http:/foo.com' is now expected
to succeed, not throw an exception. The second test for
'foo.com/bar/baz' in strict mode is correct; that's parsed in strict
mode as a truly relative path.

Change-Id: Ibc4386ba40cffea9d30417ec2720114f6819ae1c