This patch allows to configure MyISAM for 128 indexes per table.
The main problem is the key_map, wich is implemented as an ulonglong.
To get rid of the limit and keep the efficient and flexible
implementation, the highest bit is now used for all upper keys.
This means that the lower keys can be disabled and enabled 
individually as usual and the high keys can only be disabled and
enabled as a block. That way the existing test suite is still
applicable, while more keys work, though slightly less efficient.
To really get more than 64 keys, some defines need to be changed.
Another patch will address this.


include/my_bitmap.h:
  Bug#10932 - Building server with key limit of 128, makes test cases fail
  Added the declaration for a function that extends the highest bit value
  to all upper bits of a bigger bitmap.
include/myisam.h:
  Bug#10932 - Building server with key limit of 128, makes test cases fail
  Changed MI_MAX_POSSIBLE_KEY to what it was meant for.
  Added a bunch of macros to handle the MyISAM key_map.
myisam/mi_check.c:
  Bug#10932 - Building server with key limit of 128, makes test cases fail
  Changed key_map access to use the new macros.
myisam/mi_create.c:
  Bug#10932 - Building server with key limit of 128, makes test cases fail
  Changed key_map access to use the new macros.
myisam/mi_delete.c:
  Bug#10932 - Building server with key limit of 128, makes test cases fail
  Changed key_map access to use the new macros.
myisam/mi_extra.c:
  Bug#10932 - Building server with key limit of 128, makes test cases fail
  Changed key_map access to use the new macros.
myisam/mi_open.c:
  Bug#10932 - Building server with key limit of 128, makes test cases fail
  Changed key_map access to use the new macros.
  Changed pointer types from signed char* to unsigned char*.
myisam/mi_preload.c:
  Bug#10932 - Building server with key limit of 128, makes test cases fail
  Changed key_map access to use the new macros.
myisam/mi_rsame.c:
  Bug#10932 - Building server with key limit of 128, makes test cases fail
  Changed key_map access to use the new macros.
myisam/mi_rsamepos.c:
  Bug#10932 - Building server with key limit of 128, makes test cases fail
  Changed key_map access to use the new macros.
myisam/mi_search.c:
  Bug#10932 - Building server with key limit of 128, makes test cases fail
  Changed key_map access to use the new macros.
myisam/mi_update.c:
  Bug#10932 - Building server with key limit of 128, makes test cases fail
  Changed key_map access to use the new macros.
myisam/mi_write.c:
  Bug#10932 - Building server with key limit of 128, makes test cases fail
  Changed key_map access to use the new macros.
myisam/myisamchk.c:
  Bug#10932 - Building server with key limit of 128, makes test cases fail
  Changed key_map access to use the new macros.
myisam/myisamdef.h:
  Bug#10932 - Building server with key limit of 128, makes test cases fail
  Changed pointer types from signed char* to unsigned char*.
myisam/myisamlog.c:
  Bug#10932 - Building server with key limit of 128, makes test cases fail
  Changed key_map access to use the new macros.
myisam/myisampack.c:
  Bug#10932 - Building server with key limit of 128, makes test cases fail
  Changed key_map access to use the new macros.
myisam/sort.c:
  Bug#10932 - Building server with key limit of 128, makes test cases fail
  Changed key_map access to use the new macros.
mysys/my_bitmap.c:
  Bug#10932 - Building server with key limit of 128, makes test cases fail
  Added a function that extends the highest bit value
  to all upper bits of a bigger bitmap.
sql/ha_myisam.cc:
  Bug#10932 - Building server with key limit of 128, makes test cases fail
  Changed key_map access to use the new macros.
sql/sql_bitmap.h:
  Bug#10932 - Building server with key limit of 128, makes test cases fail
  Added a method that extends the highest bit value
  to all upper bits of a bigger bitmap.