(bug 45244) show correct diff revision id in diff view

This is supposed to be what is specified in the diff parameter,
or if it is 'next' then it should show the next revision after oldid.

If diff=cur, then the latest revision should be displayed, diffed against oldid.

If diff=prev, then the oldid is the version to be displayed.

Change-Id: I397332986f735e900522f3e6d2dcc7f7e335418b
Merge "(bug 45244) show correct diff revision id in diff view"