Too many page versions

[boutell]

Right now we save a version of the entire page every 5 seconds if any changes have been made. This can lead to a very large database.

We can address it by pruning out consecutive versions by the same author less than X minutes apart, once they are Y hours old.

We need to stop storing diffs and start generating them dynamically in order for the removal of intervening versions to still result in reasonable-looking diffs.