in-place rotate should indicate jpegtran failure

[derf]

https://bugs.launchpad.net/ubuntu/+source/feh/+bug/768496

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When I try to rotate an image using feh's inplace editing (right-clicking the image,
and chosing "Rotate 90 CW" for example), nothing happens. The picture does not rotate.

Feh does not display any error message, but when I run feh from the command line,
I get the following error message (the picture I'm trying to rotate is called "p1000065.jpg":

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jpegtran: can't open p1000065.jpg for writing
feh WARNING: lossless rotate: Got exitcode 1 from jpegtran. Commandline was:
jpegtran -copy all -rotate -1076465748 -outfile p1000065.jpg p1000065.jpg

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When I try to run the jpegtran command directly from the command line,
all I get is the help menu, so the command feh is trying to run isn't working for some reason.

Edited to add:
The reason for this error was that the file I was trying to rotate was read-only.
However, feh didn't give any indication of what the problem was, it just failed silently.
It would be nice if there was some kind of indication why the action failed,
or perhaps the options shouldn't be available when the picture cannot be written.