[RFC] refer to post-patch lines in whitespace warnings

When I rebase series with bad whitespace, I end up with unhelpful messages 
like:

.dotest/patch:412: trailing whitespace.
-- 
.dotest/patch:446: trailing whitespace.
-- 

These line numbers obviously refer to lines in a file that's been removed 
by the time I can do anything about it. It seems to me like the message 
would be more useful if, in the case where it leaves the working tree 
modified with the non-compliant whitespace, it gave this location rather 
than the patch's location (because, even if you have the patch still, 
you'd need to revert it first in order to be able to apply a fixed version 
anyway). Anybody see any problems with this theory?

	-Daniel
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