[Xsb-development] Yet another attributed variable change

[Terrance S. <ts...@cs...>]

I just made another change to improve the compatibility of XSB with other Prologs in its handling of attributed variables.  If a call

get_attr(X,foo,Y)

is made where X is a non variable, XSB throws an exception, while SWI, YAP, BProlog and perhaps others fail.  You  can make arguments for either behavior, but since we generally import constraint handling libraries from other Prologs, compatibility is important.

Let me know if this causes any problems.