Automatic merge from submit-queue
Validation: Make validation func return error strings
Part of an ongoing series of validation cleanups.
This centralizes the error strings next to the code that checks the error conditions. Future commits will refine the messages further and provide more utility validators.
I'm OK if this doesn't go into 1.2, but I am tired of rebasing :) I suggest commit-by-commit review, which should go pretty quickly. This was largely mechanical.
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5f2460b58c
