pmRegisterDerived return values

[Marko Myllynen <myllynen@xxxxxxxxxx>]

Hi,

In https://bugzilla.redhat.com/show_bug.cgi?id=1286733 two Python PMAPI
pmRegisterDerived related issues were reported and they were already
fixed but I think we all kind of forgot the bigger picture.

Consider this example (from the BZ):

        try:
            self.context.pmRegisterDerived("foo", "rat(disk.dev.read)")
        except:
            print self.context.pmDerivedErrStr()

Here pmDerivedErrStr returns nothing. Is this expected or should
pmDerivedErrStr be improved to return always something understandable in
case of errors?

Thanks,

-- 
Marko Myllynen