fix implicit fallthrough spelling

This commit fixes the syntax of the implicit fallthrough comments, in
order to be matched by GCC (and probably other compilers as well) with
the following regular expression:

[ \t.!]*([Ee]lse,? |[Ii]ntentional(ly)? )? fall(s | |-)?thr(ough|u)[
\t.!]*(-[^\n\r]*)?

See: https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wimplicit-fallthrough=

proxy.c

@@ -171,8 +171,8 @@ size_t remove_peer_from_torrent_proxy( ot_hash hash, ot_peer *peer ) {
   if( exactmatch ) {
     ot_peerlist *peer_list = torrent->peer_list;
     switch( vector_remove_peer( &peer_list->peers, peer ) ) {
-      case 2:  peer_list->seed_count--; /* Fall throughs intended */
+      case 2:  peer_list->seed_count--; /* Intentional fallthrough */
-      case 1:  peer_list->peer_count--; /* Fall throughs intended */
+      case 1:  peer_list->peer_count--; /* Intentional fallthrough */
       default: break;
     }
   }

trackerlogic.c

@@ -365,8 +365,8 @@ size_t remove_peer_from_torrent( PROTO_FLAG proto, struct ot_workstruct *ws ) {
   if( exactmatch ) {
     peer_list = torrent->peer_list;
     switch( vector_remove_peer( &peer_list->peers, &ws->peer ) ) {
-      case 2:  peer_list->seed_count--; /* Fall throughs intended */
+      case 2:  peer_list->seed_count--; /* Intentional fallthrough */
-      case 1:  peer_list->peer_count--; /* Fall throughs intended */
+      case 1:  peer_list->peer_count--; /* Intentional fallthrough */
       default: break;
     }
   }