Add more tests for IndexedDB exception

 - rewrite the valid checkpoints from #292
Add more tests for IDBCursor update
Add a test for IDBFactory cmp
Use 'new TypeError()'
Add more tests for IDBIndex openCursor
Add more tests for IDBIndex openKeyCursor
new test to make sure implementations send upload progress events for cross-origin requests
Tests modified for IndexedDB
Rewrite manifest.py to make including local changes safer (not very backwards compatible)
Allow running tests from an external server root.

This is needed for supporting use cases where testsuites outside
wpt are run using the server in a wpt checkout. It also changes the
manifest format in a way that causes the file path to be derived from
the url unless otherwise specified.
Make img sizes parsing test match MQ spec, add more tests
Add a baseline test for 'or'
fixup review issues
new tests for moving IFRAME with modified document inside in the DOM, asserting modifications should disappear
One test is manual and make sure the constructor test fails properply if PointerEvent isn't supported
Cleanup whitespace in MutationObserver-disconnect.html.
Step in the right test in MutationObserver-disconnect.html.
cc Renamed files (replace NNN-* with description).
cc Updated messages.json file.
Fix the README for url tests a bit.