Effects: Integrate sinon fake timers into tests. Close gh-1377.
Add unit tests for .html( number ). Close gh-1447.
Ajax: Use weak ETag header in tests

See http://en.wikipedia.org/wiki/HTTP_ETag#Strong_and_weak_validation

Close gh-1448
Fix #14579: attribute selectors with trailing spaces after an unquoted value
Manage bower dependencies with grunt-bowercopy

Tracked bower dependencies are located at "src/sizzle" and "test/libs".
The source-destination mapping is in the Gruntfile.

When updating a bower dependency, update the version in bower.json, run
`grunt bower`, and then commit the result. When adding a dependency,
update the bowercopy task accordingly.

Fixes #14615.
Closes gh-1452.