Make sure errors are propagated from init_meta

Loop on copyfd meta write, since pipes may return after partial write.

partial revert of d6d2638a and
26a25df5

The original code was already tested and working correctly.

Return the actual shared reader count when it exists, not
just the current process env's reader count.

NetBSD can only handle up to 14 chars, we were using 21. Now
we encode to 15, and for NetBSD truncate the last char.

Check again after acquiring rmutex. Avoids potential issue with
a duplicate pid coming in between initial check and rmutex.

Avoid holding rmutex for longer than necessary.

Use mti_numreaders for loop limit, not me_maxreaders.

Don't obtain reader txn before displaying reader table. Exit
after reader table if no other DB query options were given.

Dump the active slots in the reader table.

Retrieve the flags from a DB handle.

Don't count pages twice if they're already accounted in an ancestor txn.

Same fix for cursor_first/last.

Whenever we enter cursor_set() the sub-cursor's flag must be
cleared. If the new cursor position has valid subdata it will
be initialized again, if not then the sub-cursor has nothing
to point to.