Added extname function to path module that returns the extension.

doc/api.txt

@@ -1548,6 +1548,18 @@ node> require("path").filename("/foo/bar/baz/asdf/quux")
 ------------------------------------
 +
 
++path.extname(p)+::
+Return the extension of the path.  Everything after the last '.', if there
+is no '.' then it returns an empty string.  Examples:
++
+------------------------------------
+node> require("path").extname("index.html")
+".html"
+node> require("path").extname("index")
+""
+------------------------------------
++
+
 +path.exists(p, callback)+::
 Test whether or not the given path exists.  Then, call the +callback+ argument with either true or false.  Example:
 +

src/node.js

@@ -716,6 +716,11 @@ var pathModule = createInternalModule("path", function (exports) {
     return parts[parts.length-1];
   };
 
+  exports.extname = function (path) {
+      var index = path.lastIndexOf('.');
+      return index < 0 ? '' : path.substring(index);
+  };
+
   exports.exists = function (path, callback) {
     var p = posix.stat(path);
     p.addCallback(function () { callback(true); });