Use new api to get task list.

BTW, Fix following issue, 

Traceback (most recent call last):
  File "./xfdown.py", line 134, in <module>
    XFdownUi().main()
  File "./xfdown.py", line 96, in main
    self.work()
  File "./xfdown.py", line 100, in work
    xf.download(self.getSelected())
  File "/home/trinity/Workspace/xfdown/xfdown_api.py", line 111, in download
    self.gethttp(lists)
  File "/home/trinity/Workspace/xfdown/xfdown_api.py", line 306, in gethttp
    self.filehttp[num]=(re.search(r'\"com_url\":\"(.+?)\"\,\"',str).group(1))
AttributeError: 'NoneType' object has no attribute 'group'
Merge pull request #27 from shinohane/beta

Use new api to get task list.
Merge branch 'beta' of https://github.com/kikyous/xfdown into beta
更改了缓存文件的名字