Fix WIN32 -> _WIN32
For ITS#7789: Ensure mapsize >= pages in use.

Check new mapsizes against mm_last_pg.  Move
mdb_env_init_meta0() so it can set mm_last_pg earlier.
Fix SysV semaphores - repair mti_txnid.

Similar to 443a7e40c4280cfd07cbf80c5de62ea072b136e3.
ITS#7994 Access to current transaction ID.

I, David Barbour, hereby place the following modifications to OpenLDAP
Software (and only these modifications) into the public domain. Hence,
these modifications may be freely used and/or redistributed for any
purpose with or without attribution and/or other notice.
ITS#7994 fix prev commit

Strip docs promising behaviors that we don't promise to hold.
Strip MDB_txnid_t typedef.
ITS#7987 fix excessive space for single write txn
C90-compatible code for SysV semaphores
Clarify mdb_dbi_open doc

The concurrency restriction is on threads within a single process.
Multiple processes can use mdb_dbi_open without affecting each other.
Try to avoid an invalid datafile after failed init
make clean: remove *.lo
Fix MDB_APPEND doc

We actually compare the new key against the last key, to prevent
corruption.