Added HOM version of RAC lifting

- added rac_lift and associated private RACLiftProxy.
- Refactored existing -rac_liftSelector:withObjects: and rac_lift in terms of
  common functionality. Tests pass.
- Added -[NSInvocation(RACTypeParsing) rac_argumentAtIndex:] which behaves like
  -rac_returnValue.
Added specs for -rac_lift HOM
RACLiftProxy: set NULL as return value for non-object return types
Fixed copy-pasta mistake

Was -getReturnValue:, should have been -getArgument:atIndex:
Remove case for void argument type in -rac_argumentAtIndex:

Of course that case could never occur.
Corrected typo in -rac_argumentAtIndex: documentation
Added commentary to RACLiftProxy
RACLiftProxy: assert that it can only receive void or object-returning messages
Improved documentation for -rac_lift in light of changes
Factored out common behavior in RACLifting specs

Unfortunately, this doesn't bring down the line-count by much at all; but it
does at least avoid duplication of test cases.
Added spec that -rac_lift HOM should fail for messages returning primitive type
Correct typo in RAFLiftProxy assertion
Style cleanup in NSObjectRACLiftingSpec

- consistent use dot syntax
- consistent use new instead of alloc.init
Remove test for RAFLiftProxy HOM failure on primitive return types
Renamed method in <RACLiftingTestRig> for consistency with RACTestObject
Clarified documentation of <RACLiftingTestRig>
Removed no-longer-necessary method on RACTestObject

Since we're not testing failure of HOM for messages returning primitive types,
no need for this kit anymore.
Sets correct length for memmove() operation.
Merge pull request #424 from jonsterling/rac-lifting-HOM

Added HOM version of RAC message lifting
Merge pull request #440 from ndouglas/small_fix_to_RACBacktrace

Sets correct length for memmove() operation.