Fix test-require-cache-without-stat.js

This path adds an additional cache to the module system for caching the
location of previously required modules. Since it is embedded in the
loop that iterates over all require.paths, this patch also handles the
case where require.paths is being modified.

The patch also cleans up some code around it.

See: https://groups.google.com/forum/#!topic/nodejs-dev/QGGlrvLDHVs

src/node.js

@@ -166,6 +166,7 @@
     // modules in thier own context.
     Module._contextLoad = (+process.env['NODE_MODULE_CONTEXTS'] > 0);
     Module._cache = {};
+    Module._pathCache = {};
     Module._extensions = {};
     Module._paths = [];
 
@@ -216,22 +217,41 @@
       // given a path check a the file exists with any of the set extensions
       function tryExtensions(p, extension) {
         for (var i = 0, EL = exts.length; i < EL; i++) {
-          f = tryFile(p + exts[i]);
+          var filename = tryFile(p + exts[i]);
-          if (f) { return f; }
+
+          if (filename) {
+            return filename;
+          }
         }
         return false;
       };
 
+      var cacheKey = JSON.stringify({request: request, paths: paths});
+      if (Module._pathCache[cacheKey]) {
+        return Module._pathCache[cacheKey];
+      }
+
       // For each path
       for (var i = 0, PL = paths.length; i < PL; i++) {
-        var p = paths[i],
+        var basePath = path.resolve(paths[i], request);
+
         // try to join the request to the path
-            f = tryFile(path.resolve(p, request)) ||
+        var filename = tryFile(basePath);
+
+        if (!filename) {
           // try it with each of the extensions
-            tryExtensions(path.resolve(p, request)) ||
+          filename = tryExtensions(basePath)
+        }
+
+        if (!filename) {
           // try it with each of the extensions at "index"
-            tryExtensions(path.resolve(p, request, 'index'));
+          filename = tryExtensions(path.resolve(basePath, 'index'))
-        if (f) { return f; }
+        }
+
+        if (filename) {
+          Module._pathCache[cacheKey] = filename;
+          return filename;
+        }
       }
       return false;
     }

test/simple/test-require-cache-without-stat.js

@@ -24,9 +24,8 @@ fs.stat = function() {
 };
 
 // Load the module 'a' and 'http' once. It should become cached.
-
+require.paths.push(common.fixturesDir);
-var m = common.fixturesDir + '/a';
+require('a');
-require(m);
 require('http');
 
 console.log("counterBefore = %d", counter);
@@ -35,7 +34,7 @@ var counterBefore = counter;
 // Now load the module a bunch of times.
 // stat should not be called.
 for (var i = 0; i < 100; i++) {
-  require(m);
+  require('a');
 }
 
 // Do the same with a built-in module