modules/admin-full: display an error if libiwinfo is not installed

modules/admin-full/luasrc/view/admin_network/wifi_overview.htm

@@ -87,10 +87,19 @@ $Id$
 			netdevs[net:ifname()] = dev:name()
 		end
 	end
+
+	local has_iwinfo = pcall(require, "iwinfo")
 -%>
 
 <%+header%>
 
+<% if not has_iwinfo then %>
+	<div class="errorbox">
+		<strong><%:Package libiwinfo required!%></strong><br />
+		<%_The <em>libiwinfo</em> package is not installed. You must install this component for working wireless configuration!%>
+	</div>
+<% end %>
+
 <script type="text/javascript" src="<%=resource%>/cbi.js"></script>
 <script type="text/javascript">//<![CDATA[
 	var iwxhr = new XHR();