Add support for is() with multiple types.

Add ability to check if a request is one of a set number of types
by providing an array. If any type matches, then the method returns
true.

Refs #3714
Add CakeRequest::isAll().

Provides a way to test multiple request types at the same time. And
assert that all pass. This replaces longer conditionals with a terser
syntax.

Refs #3714
Merge pull request #1213 from markstory/improve-request-is

Improve CakeRequest::is()

Fixes #3714