Checkpoint: Reorder operations

[diegosalvi]

Actually checkpoint execute page manipulations as: cleanup dirty page

1. cleanup dirty pages
2. compact small pages
3. flush temporary pages

Just step 3 is strictly needed.

The process should be changed as:

1. flush temporary pages
2. cleanup dirty pages
3. compact small pages

With 3 timeout for the whole checkpoint, just cleanup phase and just compaction phase.

[diegosalvi]

Compaction & Cleanup timeouts already implemented. Remains operation reorder (with new changes could be even simpler...). Data remaining from last halfempty newpage will be used for dirty & small pages rebuild