Fix a minor issue with Bug#16206 (bdb.test failed if the tree is compiled 
without blackhole).


include/my_sys.h:
  Change declaration of my_strdup_with_length to accept const char *,
  not const byte *: in 5 places out of 6 where this function is used,
  it's being passed char *, not byte *
mysql-test/r/bdb.result:
  Remove dependency on an optional engine (updated test results).
mysql-test/t/bdb.test:
  Remove dependency on an optional engine.
mysys/my_malloc.c:
  my_strdup_with_length: const byte * -> const char *
mysys/safemalloc.c:
  my_strdup_with_length: const byte * -> const char *
sql/ha_federated.cc:
  my_strdup_with_length: const byte * -> const char *
sql/log_event.cc:
  my_strdup_with_length: const byte * -> const char *
sql/set_var.cc:
  my_strdup_with_length: const byte * -> const char *
sql/sql_class.h:
  Change db_length type to uint from uint32 (see also table.h)
sql/table.h:
  Change the type of db_length to uint from uint32: LEX_STRING uses uint for 
  length, we need a small and consistent set of types to store length to 
  minimize cast and compile failures.