frontend: add name to OFInput

Just useful for debugging.
diff --git a/loxigen.py b/loxigen.py
index 7b78f63..31214ba 100755
--- a/loxigen.py
+++ b/loxigen.py
@@ -332,7 +332,7 @@
 
     # Create the OFInput from the AST
     try:
-        ofinput = frontend.create_ofinput(ast)
+        ofinput = frontend.create_ofinput(os.path.basename(filename), ast)
     except frontend.InputError as e:
         print "Error in %s: %s" % (os.path.basename(filename), str(e))
         sys.exit(1)