[XCTEST] Use runtime instead of XCT_EXPORT macro.

Use the runtime to determine which failure API (XCTest's
`recordFailureWithDescription:inFile:atLine:expected:` or
SenTestingKit's `failWithException:`) to use, instead of using
XCT_EXPORT macro.
[XCTEST] Remove Travis test not supported on 4.6.

Cannot test KiwiXCTests until Travis supports Xcode 5 or greater.