Move the "empty search for latest" to collections

There is now a "latest" collection (or "latest_nsfw").
The feature didn't look much used, since it didn't work on many
backends.
Using collections will make it easy to support other things
like most viewed, featured, etc.
As a bonus, I added tests for every backend with the feature.

modules/cappedtv/browser.py

@@ -67,7 +67,7 @@ class IndexPage(BasePage):
                 seconds = parts[0]
             elif len(parts) == 2:
                 hours = 0
-                minutes , seconds = parts
+                minutes, seconds = parts
             elif len(parts) == 3:
                 hours, minutes, seconds = parts
             else:
@@ -78,7 +78,6 @@ class IndexPage(BasePage):
             yield video
 
 
-
 # parser for the video page
 class VideoPage(BasePage):
     def get_video(self, video=None):
@@ -118,10 +117,12 @@ class CappedBrowser(BaseBrowser):
         assert self.is_on_page(VideoPage), 'Should be on video page.'
         return self.page.get_video(video)
 
-    def search_videos(self,pattern):
-        if not pattern:
-            self.home()
-        else:
-            self.location('/search?s=%s' % (urllib.quote_plus(pattern.encode('utf-8'))))
+    def search_videos(self, pattern):
+        self.location('/search?s=%s' % (urllib.quote_plus(pattern.encode('utf-8'))))
+        assert self.is_on_page(IndexPage)
+        return self.page.iter_videos()
+
+    def latest_videos(self):
+        self.home()
         assert self.is_on_page(IndexPage)
         return self.page.iter_videos()