Perceptual Image Diff Now Implemented

[Freddie Witherden]

Hi all,

As of yesterday mathtex now uses perceptualdiff to perform bitmap
comparisons. By default the testing utility will attempt to execute
'perceptualdiff', however, it is possible to specify the exact
location/command as an argument.

Should peceptualdiff not be available mathtex will print a warning
message. Bitmap comparisons will only be performed if perceptualdiff
is available, if not then only the glyph/rect stream will be checked.

I am still tweaking the tolerances so feedback would be welcome.

Regards, Freddie.