#2587 new test failure

[Don Porter]

==== button-5.5 ConfigureButton - image handling FAILED
==== Contents of test case:

button .b -image image1
image delete image1
.b configure -image image2
image names

---- Result was:
image2 ::tk::dialog::error::image::stop
---- Result should have been (exact matching):
image2
==== button-5.5 FAILED

[Donal K. Fellows]

looks to me like the test is simply too fragile

[Pat Thoyts]

Fixed by checking for the difference between the before and after sets of images.