[Squash/Drop] Unsupported MDB_ROBUST -> EINVAL

[Do we want this?

Now users won't mistakenly think they have robust mutexes.

Unless another process like mdb_stat inited the lockfile with
another config.  Does mdb_stat need a -R(obust) flag?

OTOH a working config on one system can now EINVAL on another,
though the user could use mdb_env_set_flags() to get the EINVAL
there instead of in mdb_env_open().]

libraries/liblmdb/lmdb.h

@@ -519,7 +519,7 @@ int  mdb_env_create(MDB_env **env);
 	 *	<li>#MDB_ROBUST
 	 *		Initialize the lockfile to catch stale locks if robust mutexes
 	 *		are supported, so aborted processes will not block others.
-	 *		Ignored when another process has the environment open, and
+	 *		Ignored when another process has the environment open. Unsupported
 	 *		by liblmdb built with MDB_USE_POSIX_SEM (such as BSD systems).
 	 *		Enabled by default on Windows. Some locking slowdown on Unix.
 	 *	<li>#MDB_WRITEMAP

libraries/liblmdb/mdb.c

@@ -4389,7 +4389,7 @@ fail:
 	 *	environment and re-opening it with the new flags.
 	 */
 #define	CHANGEABLE	(MDB_NOSYNC|MDB_NOMETASYNC|MDB_MAPASYNC|MDB_NOMEMINIT)
-#define	CHANGELESS	(MDB_FIXEDMAP|MDB_NOSUBDIR|MDB_RDONLY|MDB_ROBUST| \
+#define	CHANGELESS	(MDB_FIXEDMAP|MDB_NOSUBDIR|MDB_RDONLY|ROBUST_FLAG| \
 	MDB_WRITEMAP|MDB_NOTLS|MDB_NOLOCK|MDB_NORDAHEAD)
 
 #if VALID_FLAGS & PERSISTENT_FLAGS & (CHANGEABLE|CHANGELESS)