Monty,
For the latest MariaDB 5.2, all the fixes in the latest MariaDB 5.1
are there.
The game plan is to release both once a month (first 5.1 and then
5.2). That way you can always assume that 5.2 is up to date (at least
for any bug that was fixed more than a month ago).
This is not different from MySQL 5.0 or MySQL 5.1; You can always
assume that when a new MySQL 5.1 is out, it includes all bug fixes
from 5.0.
Regards,
Monty