Version for 5.0. Committed for merge.
If the result table is one of the select tables in INSERT SELECT,
we must not disable the result tables indexes before selecting.
Now the preparation is split into two prepare methods.
The first detects the situation and defers some preparations
until the second phase.


mysql-test/r/insert_select.result:
  BUG#6034 - Error code 124:  Wrong medium type.
  The test results.
mysql-test/t/insert_select.test:
  BUG#6034 - Error code 124:  Wrong medium type.
  The test case.
sql/sql_class.h:
  BUG#6034 - Error code 124:  Wrong medium type.
  Added a new method for deferred preparation actions.
sql/sql_insert.cc:
  BUG#6034 - Error code 124:  Wrong medium type.
  If the insert table is one of the select tables, a part 
  of the result table preparations like disabling indexes
  has to be done after the select phase.
  This is now done in the new method select_insert::prepare2().
sql/sql_select.cc:
  BUG#6034 - Error code 124:  Wrong medium type.
  The result table preparation is now split into prepare() and
  prepare2(). Disabling indexes and other preparation stuff
  is deferred until after the selection phase.