Improved error for algo renaming in counters

The causes used to always be "Wrong counters" whatever happened. Now various cases are distinguished :

• Missing/Extra algos with counters
• Unsafe algorithm renaming
• Safe algorithm renaming
• Algo renaming with wrong counters

Note that the notion of safety is relative. It only means that both ref and output have one single algo with given name prefix (hash removed), and that all counters for the 2 are perfectly matching.