More doc for MDB_NORDLOCK
s/MDB_NORDLOCK/MDB_NOLOCK/

Leave all lock management to the caller.
Set subDB DBI=parent DBI, fix MDB_DUPSORT delete.

xcursor DBIs were parent DBI+1 for debugging. Instead output
-(parent DBI).  Fixes a crash in mdb_cursor_del0()'s xcursor
tracking, it forgot to subtract 1 for C_SUB cursors.
Set MDB_xcursor DB_DIRTY, clear md_name.

Both were unused and md_name was unmaintained -- except
mdb_cursor_touch(xcursor) would abuse md_name as a key to
touch MAIN_DBI if it could somehow get passed ! DB_DIRTY.
Optimize code holding reader mutex
mdb_node_add(): Plug page leak when MDB_PAGE_FULL.

Do not fail after mdb_page_new() succeeds.
mdb_cursor_sibling(): Fix error result
Maintain MDB_cursor.mc_top
Add Caveat: Readers need write access. Whitespace.
ITS#7715 always set filesize for WRITEMAP
Fix mdb_env_set_mapsize()

Don't allow shrinking below minimum size for an already open env.
ITS#7718 invalidate cursor when DB gets emptied
ITS#7722 fix page_merge for collapsing root

Other cursors being fixed up are not necessarily height 1.
Add MDB_USE_HASH

There may be other uses for it besides semaphore names.
ITS#7589 avoid wasting space in mdb_page_split

Also, check the split point on branch pages as well as leaf pages.
ITS#7589 Cleanup unneeded vars in prev patch
ITS#7589 Fix typo in prev commit
ITS#7589 silence warnings