Fix TypeError: string arg required in find_links()

Fixes #317.

linkcheck/parser/__init__.py

@@ -130,7 +130,7 @@ def find_links (url_data, callback, tags):
     handler.parser = parser
     # parse
     try:
-        content = url_data.get_content()
+        content = url_data.get_raw_content()
         with parse_mutex:
             parser.feed(content)
             parser.flush()

tests/checker/data/utf8.html.result

@@ -0,0 +1,5 @@
+url file://%(curdir)s/%(datadir)s/utf8.html
+cache key file://%(curdir)s/%(datadir)s/utf8.html
+real url file://%(curdir)s/%(datadir)s/utf8.html
+name %(datadir)s/utf8.html
+valid