Hardcode "ignore" method

The "ignore" method used to force the opening of the file. Some editors (emacs) create symbolic links to use as synchronization locks. Those links have an extension that matches the opened file, but the links themselves do not point to an existing file, thus causing Babel to attempt to open a file that does not exist.

This fix skips opening of a file altogether when using the method "ignore" in the mapping file.

babel/messages/extract.py

@@ -236,9 +236,12 @@ def extract_from_file(method, filename, keywords=DEFAULT_KEYWORDS,
     :returns: list of tuples of the form ``(lineno, message, comments, context)``
     :rtype: list[tuple[int, str|tuple[str], list[str], str|None]
     """
+    if method == 'ignore':
+        return []
+
     with open(filename, 'rb') as fileobj:
-        return list(extract(method, fileobj, keywords, comment_tags, options,
-                            strip_comment_tags))
+        return list(extract(method, fileobj, keywords, comment_tags,
+                            options, strip_comment_tags))
 
 
 def extract(method, fileobj, keywords=DEFAULT_KEYWORDS, comment_tags=(),