Fix NSInputStream replacement for iOS 7 by forwarding respondsToSelector: to the captured stream object

git-svn-id: http://gtm-http-fetcher.googlecode.com/svn/trunk@135 b3aa69f0-f65c-a609-0a27-78855af037c1
Update fetcher unit tests to XCTest.

git-svn-id: http://gtm-http-fetcher.googlecode.com/svn/trunk@136 b3aa69f0-f65c-a609-0a27-78855af037c1