[packagekit] optimize percentage in PackageKitBaseBackend

[Mounir Lamouri]

yum backend has a small optimization to prevent percentage message to
be sent too many times, it adds this condition before calling
percentage from PackageKitBaseBackend:
if percent == 0 or percent > self.percentage_old:

I would like to know if it is possible to add this optimization
directly into PackageKitBaseBackend. This optimization needs to add a
member variable to PackageKitBaseBackend.

Thanks,
Mounir