[bjhuang]

some bugs about creating new hosters:
1. did not create or check thumbnails subdirectory of hoster on xml import.
2. thumbnails may not be JPG. thumbnails could be saved in other formats, but it looks for JPG on display.
3. i tried to "return $this->url" in fetch_videourl function but failed. in some sites, the url just can not be formatted simply with videoid.
4. if tags exceed limit, no tag will be saved. should be sliced down to the limit automatically.

suggestions:
1. what can i do if there is no thumbnail?
2. a lot of temp files vbuploadxxxx left in the root dir. plz remove them or create them in a tmp dir.