Added Support for Ubuntu 15.04 in OS detect code.

Till Brehm

2015-05-06 ed46b479b558fd5dba53f4bf79caf360130ba4ce

 install/lib/install.lib.php

@@ -86,6 +86,9 @@
         $mainver = array_filter($mainver);
         $mainver = current($mainver).'.'.next($mainver);
         switch ($mainver){
         case "15.04":
            $relname = "(Vivid Vervet)";
            break;
         case "14.10":
            $relname = "(Utopic Unicorn)";
            break;