Support before/after suite in Objective-C

Fixing #63 from 32,000 feet over Hanover.
Nimble.xcodeproj: add missing headers

Inexplicably, the project appeared to be building just fine as of
712a3e5029e42911a5988eeee54898edafeb3d27. At some point Xcode must have
reverted to a previous version, and that version was committed.