memset, memcpy, sizeof consistency fixes

Just as with the OPENSSL_malloc calls, consistently use sizeof(*ptr)
for memset and memcpy.  Remove needless casts for those functions.
For memset, replace alternative forms of zero with 0.

Reviewed-by: Richard Levitte <levitte@openssl.org>

test/heartbeat_test.c

@@ -211,7 +211,7 @@ static int execute_heartbeat(HEARTBEAT_TEST_FIXTURE fixture)
      * Make a local copy of the request, since it gets overwritten at some
      * point
      */
-    memcpy((char *)sent_buf, (const char *)payload, sizeof(sent_buf));
+    memcpy(sent_buf, payload, sizeof(sent_buf));
 
     return_value = fixture.process_heartbeat(s, s->rlayer.rrec.data,
         s->rlayer.rrec.length);