WL#1210: Support index organised MyISAM tables

In some cases special form of tables which match the following criteria are useful:
   - They have only one key
   - This key spans all columns 

ie:
 create table value_set(i int not null primary key)


For such tables you can skip creation of data files (MYD) which can
significantly speed things up.

The problem of such tables is - you do not have a way to rebuild index so they 
are only usable for temporary object storage.  

At least it is safe to enable such support for TEMPORARY tables (Monty claims
MyISAM has such support already and it is used for some internal tables)