XCTest support for otest-shim & OCUnit* classes.

* Added XCTestLog_* functions in otest-shim.m. These are analogous to their SenTestLog_* counterparts, and call XCToolLog_*.
* Added XCTest.h to xctool proj
* Updated OCUnit* classes to use TestingFramework. This enables XCTest support for these classes.
* Additional information has been added to the TestingFramework dictionary:
  * iOS and OS X test runner executable names
  * the argument key for inverting scope
  * the argument key for filtering test cases
* Renamed the python script wrapping `ld` to reflect the fact that it now wraps `cc` as well.
* Removed the exception class name from reporter.m & update tests.
  (This is necessary because XCTest does not expose the NSException instance like SenTestingKit.
  Thus, XCTest does not know what the exception class name is.)
* Added test `testRunTestsFailsWhenSDKIsIPHONEOS_XCTest`
* Added import to <execinfo.h> in test projects to get rid of compiler warnings