Use revision timestamp instead of wfTimestampNow()

In some circumstances the revision id can be constructed during one
second and the moderation timestamp set during the next second. This
causes a mismatch between the timestamp embedded in the revision and
the reported moderation time.

This patch changes the revisions to source their moderation timestamp
directly from the revision id.

Change-Id: Ib05da5063c45853d2325b1e14193bfb025c7ad60
Merge "Use revision timestamp instead of wfTimestampNow()"