fix test suite to pass on windows

On windows, the sync of the second cloned repo to origin failed, because
synced/master was a non-fast-forward. This may be a bug of its own, but
it's not the issue that this test was intended to test, so disconnect
the repos from origin before syncing.

doc/bugs/test_failures_on_window_for_5.20131118.mdwn

@@ -19,6 +19,4 @@ windows 7, NTFS = 2 FAILs
 
 see attachment for full log of git annex test output
 
-> I am seeing the same 2 failures now (I used to see a lot more!)
-> and have put some analysis in [[todo/windows_support]] about them.
-> --[[Joey]]
+> Reproduced and [[fixed|done]]. --[[Joey]]