[RESEND][PATCH] Fix diffing unmodified against modified remote file

Seems as if the first message from my work account didn't get
through to the ML. Re-sending from my personal account as it
should be known already.

--
Hi,
When having an unmodified but out-of-date local file which is to
be diffed with an updated remote file (via "Check for
modifications" -> "Check repository" -> "Compare with HEAD and
BASE"), the resulting diff window is confusing the local and
remote files. The left side will display the read-only local file
while the right side will display the writable remote file, which
is obviously wrong.
The attached patch fixes the issue.
Regards
Patrick
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Patrick Steinhardt, Entwickler
elego Software Solutions GmbH, http://www.elego.de
Gebäude 12 (BIG), Gustav-Meyer-Allee 25, 13355 Berlin, Germany
Sitz der Gesellschaft: Berlin, USt-IdNr.: DE 163214194
Handelsregister: Amtsgericht Charlottenburg HRB 77719
Geschäftsführer: Olaf Wagner