Improve parsing support for OPML files

Ignore the case for file types, so that OPML files
with UPPERCASE type attributes also work (this is
the way ziepod and other apps write OPML files).

src/gpodder/opml.py

@@ -61,7 +61,7 @@ class Importer(object):
     contains workarounds to support odeo.com feeds.
     """
 
-    VALID_TYPES = ( 'rss', 'link' )
+    VALID_TYPES = ('rss', 'link')
 
     def __init__( self, url):
         """
@@ -76,7 +76,12 @@ def __init__( self, url):
                 doc = xml.dom.minidom.parseString(util.urlopen(url).read())
 
             for outline in doc.getElementsByTagName('outline'):
-                if outline.getAttribute('type') in self.VALID_TYPES and outline.getAttribute('xmlUrl') or outline.getAttribute('url'):
+                # Make sure we are dealing with a valid link type (ignore case)
+                otl_type = outline.getAttribute('type')
+                if otl_type is None or otl_type.lower() not in self.VALID_TYPES:
+                    continue
+
+                if outline.getAttribute('xmlUrl') or outline.getAttribute('url'):
                     channel = {
                         'url': outline.getAttribute('xmlUrl') or outline.getAttribute('url'),
                         'title': outline.getAttribute('title') or outline.getAttribute('text') or outline.getAttribute('xmlUrl') or outline.getAttribute('url'),