Bit type: fix for create_field::create_field().

sql/field.cc:
  Bit type: fix for create_field::create_field().
  We should return saved length in case of Field_bit_as_char.

mysql-test/r/type_bit_innodb.result

@@ -380,3 +380,25 @@ drop table t1;
 create table t1(a int, b bit not null) engine=innodb;
 alter table t1 add primary key (a);
 drop table t1;
+create table t1 (a bit, b bit(10)) engine=innodb;
+show create table t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` bit(1) default NULL,
+  `b` bit(10) default NULL
+) ENGINE=InnoDB DEFAULT CHARSET=latin1
+alter table t1 engine=heap;
+show create table t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` bit(1) default NULL,
+  `b` bit(10) default NULL
+) ENGINE=MEMORY DEFAULT CHARSET=latin1
+alter table t1 engine=innodb;
+show create table t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` bit(1) default NULL,
+  `b` bit(10) default NULL
+) ENGINE=InnoDB DEFAULT CHARSET=latin1
+drop table t1;

mysql-test/t/type_bit_innodb.test

@@ -121,3 +121,15 @@ drop table t1;
 create table t1(a int, b bit not null) engine=innodb;
 alter table t1 add primary key (a);
 drop table t1;
+
+#
+# altering tables
+#
+
+create table t1 (a bit, b bit(10)) engine=innodb;
+show create table t1;
+alter table t1 engine=heap;
+show create table t1;
+alter table t1 engine=innodb;
+show create table t1;
+drop table t1;

sql/field.cc

@@ -8358,7 +8358,9 @@ create_field::create_field(Field *old_field,Field *orig_field)
     break;
 #endif
   case FIELD_TYPE_BIT:
-    length= ((Field_bit *) old_field)->bit_len + length * 8;
+    length= (old_field->key_type() == HA_KEYTYPE_BIT) ?
+            ((Field_bit *) old_field)->bit_len + length * 8 :
+            ((Field_bit_as_char *) old_field)->create_length;
     break;
   default:
     break;

sql/field.h

@@ -1313,9 +1313,8 @@ class Field_bit :public Field {
 
   
 class Field_bit_as_char: public Field_bit {
-protected:
-  uchar create_length;
 public:
+  uchar create_length;
   Field_bit_as_char(char *ptr_arg, uint32 len_arg, uchar *null_ptr_arg,
                     uchar null_bit_arg, uchar *bit_ptr_arg, uchar bit_ofs_arg,
                     enum utype unireg_check_arg, const char *field_name_arg,