Deprecate `F2.isLocalRequest`

[montlebalm]

As an F2 developer, I want to depreciate F2.isLocalRequest because I want F2 to contain only methods relevant to consumers.

Is F2.isLocalRequest useful enough to be attached to the core library? F2 is perched between being a general convenience library and a specialized app integration library. My preference is to move F2 away from the former and more solidly into the latter category.

[markhealey]

Good thinking, though isLocalRequest exists as part of the XHR config.

[brianbaker]

this is pretty heavily used as a part of the XHR config that @markhealey mentioned so we'll leave it in the API