Currently, only TABLE_TYPE is tested, and if wrong or unspecified,
is replaced by the default value DOS.

- Test on type was moved from create to pre_create
- pre_create is now called unconditionally and must return true
  on error and false otherwise.
- Warnings are produced if the table type was changed.
- The errors have specific error messages (instead of being warnings
  with an error message telling that a table must have columns)

Modified:
ha_connect.cc
ha_connect.h
handler.h
sql_table.cc