ITS#7994 fix prev commit

Strip docs promising behaviors that we don't promise to hold.
Strip MDB_txnid_t typedef.

libraries/liblmdb/lmdb.h

@@ -226,9 +226,6 @@ typedef struct MDB_env MDB_env;
  */
 typedef struct MDB_txn MDB_txn;
 
-/** @brief Unique identifier for an active or recent transaction. */
-typedef size_t MDB_txnid_t;
-
 /** @brief A handle for an individual database in the DB environment. */
 typedef unsigned int	MDB_dbi;
 
@@ -451,7 +448,7 @@ typedef struct MDB_envinfo {
 	void	*me_mapaddr;			/**< Address of map, if fixed */
 	size_t	me_mapsize;				/**< Size of the data memory map */
 	size_t	me_last_pgno;			/**< ID of the last used page */
-	MDB_txnid_t  me_last_txnid;		/**< ID of the last committed transaction */
+	size_t  me_last_txnid;		/**< ID of the last committed transaction */
 	unsigned int me_maxreaders;		/**< max reader slots in the environment */
 	unsigned int me_numreaders;		/**< max reader slots used in the environment */
 } MDB_envinfo;
@@ -953,18 +950,16 @@ int  mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **
 	 */
 MDB_env *mdb_txn_env(MDB_txn *txn);
 
-	/** @brief Return the transaction's #MDB_txnid_t
+	/** @brief Return the transaction's ID.
 	 *
 	 * This returns the identifier associated with this transaction. For a
 	 * read-only transaction, this corresponds to the snapshot being read;
-	 * concurrent readers will frequently have the same transaction ID. For
+	 * concurrent readers will frequently have the same transaction ID.
-	 * a write transaction, this is always the snapshot read plus one. When
-	 * a write transaction aborts, the next transaction ID will be reused.
 	 *
 	 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
 	 * @return A transaction ID, valid if input is an active transaction.
 	 */
-MDB_txnid_t mdb_txn_id(MDB_txn *txn);
+size_t mdb_txn_id(MDB_txn *txn);
 
 	/** @brief Commit all the operations of a transaction into the database.
 	 *

libraries/liblmdb/mdb.c

@@ -2775,10 +2775,10 @@ mdb_txn_env(MDB_txn *txn)
 	return txn->mt_env;
 }
 
-MDB_txnid_t
+size_t
 mdb_txn_id(MDB_txn *txn)
 {
-    if(!txn) return (txnid_t)-1;
+    if(!txn) return 0;
     return txn->mt_txnid;
 }