DB-785 add a txn api to check if a txn is prepared

buildheader/make_tdb.cc

@@ -585,6 +585,7 @@ static void print_db_txn_struct (void) {
         "uint64_t (*id64) (DB_TXN*)",
         "void (*set_client_id)(DB_TXN *, uint64_t client_id)",
         "uint64_t (*get_client_id)(DB_TXN *)",
+        "bool (*is_prepared)(DB_TXN *)",
 	NULL};
     sort_and_dump_fields("db_txn", false, extra);
 }

src/ydb_txn.cc

@@ -421,6 +421,11 @@ static int toku_txn_discard(DB_TXN *txn, uint32_t flags) {
     return 0;
 }
 
+static bool toku_txn_is_prepared(DB_TXN *txn) {
+    TOKUTXN ttxn = db_txn_struct_i(txn)->tokutxn;
+    return toku_txn_get_state(ttxn) == TOKUTXN_PREPARING;
+}
+
 static inline void txn_func_init(DB_TXN *txn) {
 #define STXN(name) txn->name = locked_txn_ ## name
     STXN(abort);
@@ -437,6 +442,7 @@ static inline void txn_func_init(DB_TXN *txn) {
     SUTXN(discard);
 #undef SUTXN
     txn->id64 = toku_txn_id64;
+    txn->is_prepared = toku_txn_is_prepared;
 }
 
 //