LSM: fix the check for the maximum number of cursors that could be required for snapshot isolation updates.  The visibility check was backwards, so we almost always only opened a single cursor.
Cherry pick Sue's sync configuration changes, so develop matches the fine-grained-durability branch.
Check for the existence of the O_DSYNC flag, fall back to O_SYNC, or output an error if neither is available.
Rename hard-coded "sync" config key to "checkpoint_snyc" in test/format.