After merge fixes

Use server character set if --default-character-set is not used
Added convert_string() for more efficient alloc+character-set convert of strings

mysql-test/t/lock_tables_lost_commit.test

@@ -4,7 +4,9 @@ connect (con1,localhost,root,,);
 connect (con2,localhost,root,,);
 
 connection con1;
+--disable_warnings
 drop table if exists t1;
+--enable_warnings
 create table t1(a int) type=innodb;
 lock tables t1 write;
 insert into t1 values(10);