AssignableToTypeOf returns false without error if exactly one of actual or expected is nil.

[nwmahoney]

Fixes #280.

cc @rowanjacobs

[blgm]

With this change:

Expect(nil).To(BeAssignableToTypeOf(nil)) // Error
Expect(17).To(BeAssignableToTypeOf(nil))  // OK
Expect(nil).To(BeAssignableToTypeOf(17))  // OK

I think it should be:

Expect(nil).To(BeAssignableToTypeOf(nil)) // Error
Expect(17).To(BeAssignableToTypeOf(nil))  // Error
Expect(nil).To(BeAssignableToTypeOf(17))  // OK

The matcher should be able to cope with whatever ends up in the Expect(). For other situations you should either:

• check that it's assignable to a non-nil type, OR
• check that is nil using the BeNil() matcher

Any thoughts?

[rowanjacobs]

Done!