As part of the project to start storing versioned information on disk in WiredTiger, we are going to save three timestamps to checkpoints - so the version information for the tree can be considered in aggregate without reading the tree.

We will save the oldest start timestamp, newest start timestamp and newest stop timestamp of any cell on any page in the tree. This will happen naturally, it's essentially a copy of the aggregate values for the btree root page.

WT-4491 has the changes for adding versioned information to address blocks, this ticket will hold the changes for adding versioned information to checkpoints.