Better unicode error.

Cython/Compiler/Main.py

@@ -149,10 +149,12 @@ class Context:
                 filename_encoding = sys.getdefaultencoding()
             name = source_filename.decode(filename_encoding)
 
+        try:
             s = PyrexScanner(f, name, source_encoding = f.encoding,
                              type_names = type_names, context = self)
-        try:
             tree = Parsing.p_module(s, pxd, full_module_name)
+        except UnicodeDecodeError, msg:
+            error((name, 0, 0), "Decoding error, set coding=<encoding-name> at top of source (%s)" % msg)
         finally:
             f.close()
         if Errors.num_errors > 0: