Change count to a double, this avoid overflow.

Currently, word counts get up to 16 million, and then stop counting.
Remove brain-damage
Add a note...
Fix type conflicts in null truth value
Fix type conflict in indefniite truth value
Try to fix dependencies.

For some reason, AtomSpaceBenchmark.o never gets rebuilt. Never.
Even when it needs to be.  I can't figure it out, but maybe this will
fix it!?
Fix type signatures.

Changing the types on the truth value broke this test case, because
it incorrectly assumed floats.
Fix a shared-pointer race condition.

I beleive that this should fix the crash in the SQL persistance backend.
Do the TODO so that the test case doesn't crash.

New behaviour when the count became double-precision.
Atomic access: misse a spot.

During previous changes, I missed this one, somehow.