Error if no backend clusters support reservations.

www/aptui/list-reservations.php

@@ -65,6 +65,10 @@ else {
         $amlist[$aggregate->nickname()] = $aggregate->urn();
     }
 }
+if (!count($amlist)) {
+    SPITUSERERROR("No clusters support reservations.");
+    exit();
+}
 echo "<script type='text/plain' id='amlist-json'>\n";
 echo htmlentities(json_encode($amlist));
 echo "</script>\n";

www/aptui/reserve.php

@@ -105,6 +105,10 @@ elseif (isset($debug) && $debug) {
 else {
     $ams = Aggregate::SupportsReservations();
 }
+if (!count($ams)) {
+    SPITUSERERROR("No clusters support reservations.");
+    exit();
+}
 $amlist  = array();
 while (list($index, $aggregate) = each($ams)) {
     $urn = $aggregate->urn();