Remove BOM in imports.

Modified tests to run against a copy of the test files with BOMs inserted
into each .less and .css file (the copies are generated automatically if
the /test/less-bom folder doesn't exist or is empty).

lib/less/import-manager.js

@@ -68,7 +68,7 @@ module.exports = function(environment) {
 
         var loadFileCallback = function(loadedFile) {
             var resolvedFilename = loadedFile.filename,
-                contents = loadedFile.contents;
+                contents = loadedFile.contents.replace(/^\uFEFF/, '');
 
             // Pass on an updated rootpath if path of imported file is relative and file
             // is in a (sub|sup) directory