Backport r58757, r58758, r58759.
Undoes incorrect dbtables fix and errant strdup introduced as
described below:

r58757 | gregory.p.smith | 2007-11-01 14:08:14 -0700 (Thu, 01 Nov 2007) | 4 lines

Fix bug introduced in revision 58385.  Database keys could no longer
have NULL bytes in them.  Replace the errant strdup with a
malloc+memcpy.  Adds a unit test for the correct behavior.

r58758 | gregory.p.smith | 2007-11-01 14:15:36 -0700 (Thu, 01 Nov 2007) | 3 lines

Undo revision 58533 58534 fixes.  Those were a workaround for
a problem introduced by 58385.

r58759 | gregory.p.smith | 2007-11-01 14:17:47 -0700 (Thu, 01 Nov 2007) | 2 lines

false "fix" undone as correct problem was found and fixed.
diff --git a/Modules/_bsddb.c b/Modules/_bsddb.c
index 195132e..999e302 100644
--- a/Modules/_bsddb.c
+++ b/Modules/_bsddb.c
@@ -432,11 +432,13 @@
          * the code check for DB_THREAD and forceably set DBT_MALLOC
          * when we otherwise would leave flags 0 to indicate that.
          */
-        key->data = strdup(PyString_AS_STRING(keyobj));
+        key->data = malloc(PyString_GET_SIZE(keyobj));
         if (key->data == NULL) {
             PyErr_SetString(PyExc_MemoryError, "Key memory allocation failed");
             return 0;
         }
+        memcpy(key->data, PyString_AS_STRING(keyobj),
+               PyString_GET_SIZE(keyobj));
         key->flags = DB_DBT_REALLOC;
         key->size = PyString_GET_SIZE(keyobj);
     }