Check bad dates and redirect, instead of 404ing, as necessary and appropriate. 
Adds query, conditional, and canonical Unit Tests.

Props kovshenin, SergeyBiryukov, DrewAPicture.
Fixes #10935.



git-svn-id: https://develop.svn.wordpress.org/trunk@25280 602fd350-edb4-49c9-b593-d223f7449a82