Allow placing routing restrictions on tunnel/bridge entrance/exit signals

No reserve through support

docs/landscape_grid.html

@@ -287,7 +287,7 @@ the array so you can quickly see what is used and what is not.
       <td class="caption">tunnel entrance</td>
       <td class="bits" rowspan=3><span class="free">OOO</span> <span class="used" title="Owner">XXXXX</span></td>
       <td class="bits"><span class="patch-pool" title="Tunnel index on pool (or overflow sentinel)">PPPP PPPP PPPP PPPP</span></td>
-      <td class="bits" rowspan=4><span class="rearrange" title="Owner of tram (road only; a rearrangement can free some of these bits)">XXXX</span> <span class="free">OOOO</span><br /><span class="free">OO</span> <span class="patch" title="Entrance/exit signal aspects (rail only)">PPPPPP</span></td>
+      <td class="bits" rowspan=4><span class="rearrange" title="Owner of tram (road only; a rearrangement can free some of these bits)">XXXX</span> <span class="free">OOOO</span><br /><span class="free">O</span><span class="patch" title="Routing restrictions present on entrance/exit signal(s)">P</span> <span class="patch" title="Entrance/exit signal aspects (rail only)">PPPPPP</span></td>
       <td class="bits"><span class="free">OO</span><span class="used" title="Road type">XX XXXX</span></td>
       <td class="bits"><span class="used" title="Bridge or tunnel bit">O</span><span class="patch" title="Signal simulation mode (rail only)">PP</span><span class="rearrange" title="PBS reservation (rail; a rearrangement can free some of these bits)">X</span> <span class="used" title="Transport type">XX</span> <span class="used" title="Direction of the tunnel/bridge">XX</span></td>
       <td class="bits"><span class="patch" title="PBS mode, exit signal state">PP</span><span class="free">OO OO</span><span class="patch" title="Semaphore/light mode, entrance signal state">PP</span></td>