Automatically checking regtests (was: Re: Minor releases?)

[Michael Käppler]

[CC to -devel]
> (nobody checks the regression tests for each release, for example
> -- and that's trivially done with a web browser!)
>   
That reminds me of an idea I recently had: Wouldn't it be possible to 
automatically generate a sort of "checksum" for each regression-test 
output-file and compare it with the former releases? I know that every 
little change in the pdf appearance would lead to a warning then.
But I'm sure there is a way to do not just "md5sum 
regression-test-foo.pdf" but create a "difference score" by comparing 
the two pdfs.
Ideally, this would output to a list like:

foo1.pdf - 0
foo2.pdf - 13
foo3.pdf - 142
foo4.pdf - 0
(...)

Then the dev's can mark the foo3.pdf like Jerry R. Ehman's wow signal... 
;) I mean, this would give a priority for checking, when e.g. values > 
100 are urgent to control.

Cheers,
Michael