Cleanup for handlerton structure to allow for loadable engine work. This is the first in a series of patches. 


sql/examples/ha_archive.cc:
  Now declared externally.
sql/examples/ha_example.cc:
  Now declared externally
sql/examples/ha_tina.cc:
  Now declared externally
sql/ha_berkeley.cc:
  Now declared externally
sql/ha_blackhole.cc:
  Now declared externally
sql/ha_federated.cc:
  Now declared externally.
sql/ha_heap.cc:
  Now declared externally.
sql/ha_innodb.cc:
  Now declared externally.
sql/ha_myisam.cc:
  Now declared externally
sql/ha_myisammrg.cc:
  Now declared externally.
sql/ha_ndbcluster.cc:
  Now declared externally.
sql/handler.cc:
  Changes for eventual loadable engines. This will allow us to gain faster access to the handlerton (eventually this will just be a handlteron array).
sql/handler.h:
  New alias structure and change to show_table_st to place handlerton in the structure.