The attached change set adjusts the attribute exclusion code
to detect and reject incompatible attributes before attribute
handlers are called to have a chance to make changes despite
the exclusions.  The handlers are not run when a conflict is
found.

Tested on x86_64-linux.  I expected the fallout to be bigger
but only a handful of tests needed adjusting and the changes
all look like clear improvements.  I.e., conflicting attributes
that diagnosed as being ignored really are being ignored as one
would expect.

Martin