Approver logs spurious conflicts

When an import queue entry matches multiple templates based on path and origin, the approver now logs a warning instead of crashing.

But it logs too many conflicts. Take this one for example:

Found 3 templates with path 'po/apt-all.pot' for package apt (0 matched on from_sourcepackagename).

Yes, there are 3 templates with that path for that package. But they're for 3 different distroseries!

The mistake is in POTemplateSet.getPOTemplateByPathAndOrigin. It compares productseries but not distroseries when looking for its matches. For distro packages, the productseries will always be null.

A consequence of this will be that uploads for these templates won't be auto-approved, which would be a problem for the Ubuntu folks.