Ensure that when the number of cells on a page drops to zero that the freelist
and fragment counter are both cleared.  Also add evidence marks corresponding
to file-format documentation.
Add requirements marks on the built-in collating functions.
Updates to requirements tags on the mutex documentation.
Fix a benign test error on PRAGMA collation_list
introduced by a recent checkin.
Fix a typo in a requirements mark on the abs() SQL function.