refs #4476 get alter table working again in mysql 5.6.7

git-svn-id: file:///svn/mysql/tokudb-engine/tokudb-engine@48518 c7de825b-a66e-492c-adef-691d508d4ae1

storage/tokudb/ha_tokudb_alter_56.cc

@@ -326,6 +326,13 @@ ha_tokudb::check_if_supported_inplace_alter(TABLE *altered_table, Alter_inplace_
 bool 
 ha_tokudb::prepare_inplace_alter_table(TABLE *altered_table, Alter_inplace_info *ha_alter_info) {
     TOKUDB_DBUG_ENTER("prepare_inplace_alter_table");
+    tokudb_alter_ctx *ctx = static_cast<tokudb_alter_ctx *>(ha_alter_info->handler_ctx);
+    if (!ctx->alter_txn) {
+        // in 5.6, lock tables is called after check_if_supported, so the transaction is not valid in the check_if_supported
+        // function.  It should be created by now.
+        assert(transaction);
+        ctx->alter_txn = transaction;
+    }
     bool result = false; // success
     DBUG_RETURN(result);
 }