Merge branch 'patch-8' of https://github.com/bassjobsen/less.js

Author: lukeapage

lib/less/import-manager.js

@@ -40,12 +40,14 @@ module.exports = function(environment) {
             importManager.queue.splice(importManager.queue.indexOf(path), 1); // Remove the path from the queue
 
             var importedEqualsRoot = fullPath === importManager.rootFilename;
-
+            if (importOptions.optional && e) {
+			callback(null, {rules:[]}, false, null);		
+			}
+			else {
             importManager.files[fullPath] = root;
-
             if (e && !importManager.error) { importManager.error = e; }
-
             callback(e, root, importedEqualsRoot, fullPath);
+			}
         };
 
         var newFileInfo = {

lib/less/parser/parser.js

@@ -1173,7 +1173,7 @@ var Parser = function Parser(context, imports, fileInfo) {
             },
 
             importOption: function() {
-                var opt = parserInput.$re(/^(less|css|multiple|once|inline|reference)/);
+                var opt = parserInput.$re(/^(less|css|multiple|once|inline|reference|optional)/);
                 if (opt) {
                     return opt[1];
                 }