optional dependencies should be loaded in a try-catch so they are actually optional

lib/less/index.js

@@ -1,7 +1,7 @@
 var path = require('path'),
     sys = require('util'),
     url = require('url'),
-    request = require('request'),
+    request,
     fs = require('fs');
 
 var less = {
@@ -137,7 +137,10 @@ less.Parser.importer = function (file, paths, callback, env) {
     
     var isUrl = isUrlRe.test( file );
     if (isUrl || isUrlRe.test(paths[0])) {
-    
+        if (request === undefined) {
+            try { request = require('request'); }
+            catch(e) { request = null; }
+        }
         if (!request) {
             callback({ type: 'File', message: "optional dependency 'request' required to import over http(s)\n" });
             return;