pbxFile: Added defaultExtension() method for detecting extensions for build products.
diff --git a/lib/pbxFile.js b/lib/pbxFile.js
index 0d775f5..c428221 100644
--- a/lib/pbxFile.js
+++ b/lib/pbxFile.js
@@ -81,8 +81,15 @@
     return type;
 }
 
+function defaultExtension(fileRef) {
+    var extension = EXTENSION_BY_PRODUCTTYPE[fileRef.explicitFileType];
 
+    if (!extension) {
+        return;
+    }
 
+    return extension;
+}
 
 
     // dunno