Port the fix for SR-1267 back to the 2.2 branch, to fix a recent regression. (#2256)
* When obtaining the decl context for an inherited protocol conformance,
use the inherited conformance's decl context if the conformance type
does not yet have a registered class decl.
(Addresses SR-1267 and SR-1270)
* XFAIL this Foundation-dependent test on Linux.
* Correct test for 2.2 API importing.