Fixed #69. url_sanitize no longer crashes on unparsable urls.

Also optimized the code to bypass parsing when not in safe_mode and return
immediately upon failure rather than continue parsing when in safe_mode.

Note that in Python2.7+ more urls may fail than in older versions because
IPv6 support was added to urlparse and it apparently mistakenly identifies some
urls as IPv6 when they are not. Seeing this only applies to safe_mode now,
I don't really care.

markdown/inlinepatterns.py

@@ -311,20 +311,29 @@ def sanitize_url(self, url):
         `username:password@host:port`.
 
         """
+        if not self.markdown.safeMode:
+            # Return immediately bipassing parsing.
+            return url
+
+        try:
+            scheme, netloc, path, params, query, fragment = url = urlparse(url)
+        except ValueError:
+            # Bad url - so bad it couldn't be parsed.
+            return ''
+
         locless_schemes = ['', 'mailto', 'news']
-        scheme, netloc, path, params, query, fragment = url = urlparse(url)
-        safe_url = False
-        if netloc != '' or scheme in locless_schemes:
-            safe_url = True
+        if netloc == '' or scheme not in locless_schemes:
+            # This fails regardless of anything else. 
+            # Return immediately to save additional proccessing
+            return ''
 
         for part in url[2:]:
             if ":" in part:
-                safe_url = False
+                # Not a safe url
+                return ''
 
-        if self.markdown.safeMode and not safe_url:
-            return ''
-        else:
-            return urlunparse(url)
+        # Url passes all tests. Return url as-is.
+        return urlunparse(url)
 
 class ImagePattern(LinkPattern):
     """ Return a img element from the given match. """