Fix TS-1784: Calculate blocks correctly on FreeBSD

FreeBSD calculation of

    blocks = size / hw_block_size;

is wrong, because *our* *store* block size defaults to 8k.

I'm further adding comments for future reference in other code paths.

TS-1784 further reminds us that these triple (or more) code paths
are confusing at best, and should be unified.

test/review:   +1: igalic, zwoop, jpeach
backport: igalic
add backport of TS-1784 to CHANGES.
TS-1469: Manager can cause restart spins because of hardcoded FD limit

Conflicts:
	CHANGES
backport of TS-1483 (STATUS update)

test/review: igalic, zwoop, jpeach, arno
backport: igalic