Currently only implemented for OpenSSL.
Needs an option to set the criticality flag.

Lock ordering issues

Hardcoded number of queues was leftover from preliminary
work. Use connection_pool_queues.

Slightly reduce held time.

Do not access a long long as an array of longs.

op.o_extra is only used with threading

For RDONLY, don't get lockfile until we know datafile exists.
Also, don't try to create a new datafile for me_mfd if someone
deleted it after we got me_fd.

This reverts commit 87258384.

Works now, but still 2x slower. Leave disabled.

Don't compare cursors beyond their depth. (detected by valgrind)

Should allow for the possibility of future flag combos.

If a key has a single existing value, and then a put (MDB_MULTIPLE)
is done where the first of the multiple values matches the existing
value, the put would return SUCCESS without writing any of the
values. Fixed to loop to the next value as intended.

Use double DPRINTF() parenthesis, so varargs macros are not needed.
Parenthesize MDB_DEBUG, in case the user defines it as foo || bar.

Also check xcursor instead of DUPSORT, it's slightly briefer.

Checking dirty_list was insufficient after a spill
with no named databases and no positioned cursors.

countryString and telephoneNumber were missing