Human-readable changeset

[gsmolk]

It would be useful to determine how much of instance has mutated since arbitrary point in time

[ololobus]

Added ptrack_get_change_stat() in the PR:

=# select * from ptrack_get_change_stat('13/A970F418');
 files | pages |      size, MB      
-------+-------+--------------------
    12 |   144 | 1.1250000000000000
(1 row)