Move key init into mdb_env_setup_locks().
Don't create unused TLS key when read-only filesystem.
Drop internal flag MDB_ROFS, we can instead test either
!me_txns, !mt_u.reader or me_lfd==INVALID_HANDLE_VALUE.

Malloc before I/O. Avoids possible malloc error after I/O.
Don't allocate dirty & free lists when MDB_RDONLY.
Factor out code.

Don't do anything with (fake root) subpages

Fix 227329c8, don't persist
the MDB_VALID bit in db.md_flags.

Need to check NUMKEYS as well as fill threshold, when deciding
whether to change anything. Don't let the page drop below the
minimum number of keys.

This reverts commit 372b3ddb.

Original code works as designed.

mdb_dbi_close() must allow any dbi < maxdbs, since opens in an
uncommitted txn don't increment env->me_numdbs.

This reverts commit 8eef7a42.
Previous commit was correct, duplicate keys should not appear here.

Check for overflow pages, reset cursor position properly.

In APPEND don't immediately reject matching key, since this
is valid for APPENDDUP.

Append mode should *reject* keys that are too small.
Also allow APPENDDUP in mdb_put().

When fixing other cursors, must also fix their depth.

Make sure C_INITIALIZED gets set on successful call

Variables mdb_debug, mdb_debug_start were used undefined.

If the variable dkey.mv_size is non-zero, then it means dkey
contains some original data which has to be put back in the
child db, typically when the child db has just been created.

But when using MDB_MULTIPLE, if this variable has not been
reset to zero, we may come back to this section and wrongly
think that there is some original data to be taken care of.

Allow leaf pages to have only 1 key.

Causes Bus Error on SPARC

Android supports madvise but not posix_madvise

Add missing parens

It's harmful when the DB is larger than RAM.

A page must always have at least 2 keys (unless it's a root page)

We do it now... (coalescing freelist entries in page_alloc)