Implementing pre_create option test and setting of default values.

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

sql/handler.h

@@ -1932,8 +1932,8 @@ public:
   /* ha_ methods: pubilc wrappers for private virtual API */
   
   /* Added by O. Bertrand */
-  virtual bool pre_create(THD *thd, void *crt_info, void *alt_info)
-                          {return true;}
+  virtual bool pre_create(THD *thd, HA_CREATE_INFO *crt_info, void *alt_info)
+                          {return false;}
   
   int ha_open(TABLE *table, const char *name, int mode, uint test_if_locked);
   int ha_index_init(uint idx, bool sorted)