Added tests for native HTML5 validation. Disabled HTML5Number,
HTML5Date, etc. constraints. They are not validation constraints, but
data types. The browser doesn't even let you enter invalid values. Also
the typeMismatch flag is only set for type="url" or type="email", so
these constraints don't really even make sense. I haven't removed them
outright (just commented out), but I think they'll probably end up going
away at some point. Why they don't exist should probably be clarified in
the documentation.