Fix equivalence tests for request and response descriptors.
Simplify testing for pathPattern and keyPath equality per segiddins' suggestion.
Fix equivalence test for property mappings which may also have nil string attributes in the case of relationship mappings.
Merge branch 'equivalence-fix' of https://github.com/alexleigh/RestKit into alexleigh-equivalence-fix

Conflicts:
	Code/ObjectMapping/RKPropertyMapping.m
	Vendor/SOCKit
Merge branch 'alexleigh-equivalence-fix' into development