Bit type: code clean-up.

sql/field.h:
  Field_bit_as_char::size_of() added - we use it in the ::new_key_field().
sql/sql_table.cc:
  We have to set pack_flag for bit fields in the mysql_prepare_table()
  as we use it in the create_length_to_internal_length().

sql/field.h

@@ -1321,6 +1321,7 @@ public:
                     enum utype unireg_check_arg, const char *field_name_arg,
                     struct st_table *table_arg);
   enum ha_base_keytype key_type() const { return HA_KEYTYPE_BINARY; }
+  uint size_of() const { return sizeof(*this); }
   int store(const char *to, uint length, CHARSET_INFO *charset);
   int store(double nr) { return Field_bit::store(nr); }
   int store(longlong nr) { return Field_bit::store(nr); }

sql/sql_table.cc

@@ -563,9 +563,9 @@ int prepare_create_field(create_field *sql_field,
     sql_field->pack_flag=f_settype((uint) sql_field->sql_type);
     break;
   case FIELD_TYPE_BIT:
-    sql_field->pack_flag= f_bit_as_char(sql_field->pack_flag) ? 
-                          FIELDFLAG_NUMBER | FIELDFLAG_TREAT_BIT_AS_CHAR :
-                          FIELDFLAG_NUMBER;
+    /* 
+      We have sql_field->pack_flag already set here, see mysql_prepare_table().
+    */
     break;
   case FIELD_TYPE_NEWDECIMAL:
     sql_field->pack_flag=(FIELDFLAG_NUMBER |
@@ -773,6 +773,7 @@ static int mysql_prepare_table(THD *thd, HA_CREATE_INFO *create_info,
 
     if (sql_field->sql_type == FIELD_TYPE_BIT)
     { 
+      sql_field->pack_flag= FIELDFLAG_NUMBER;
       if (file->table_flags() & HA_CAN_BIT_FIELD)
         total_uneven_bit_length+= sql_field->length & 7;
       else