YoutubeIE: reuse instances of InfoExtractors (closes #998)

When a IE is added to the list, it's also added to a dictionary. When a IE is requested it first looks in the dictionary and if there's no instance it will create a new one.

That way _real_initialize is only called once for each IE, saving time if it needs to login for example.
fix bug: kankan extractor not support http://vod.kankan.com/v/70/70309.shtml
add an extractor for tv.sohu.com
use ..utils/clean_html()
Add some verbosity when reporting finished downloads

For example:

    [download] Resuming download at byte 1868140
    [download] Destination: Entry #1-Bn59FJ4HrmU.flv
    [download] 100% of 3.27MiB in 4s

This format is meant to somewhat mirror the behavior of wget(1) when reporting finished downloads:

    100%[==================>] 54,836,682   788KB/s   in 74s

    2013-08-04 12:32:05 (728 KB/s) - 'google-chrome-stable_current_x86_64.rpm' saved [54836682/54836682]
fix parse title bug
changes
improve sohu extractor
add an aes implementation
 YoupornIE: Add support for hd videos and update Test
Update AddAnime.py
Initial slash in Google+ photos link was removed
Merge pull request #1324 from whydoubt/fix_gplus

Initial slash in Google+ photos link was removed
Revert "Install our own HTTPS handler as well (#1309)"

This reverts commit 36399e85765a6a04fd84126264af75382fcfd1f6 and fixes #1322.
Delete default user agent (Fixes #1309)
release 2013.08.28
[cnn] Allow more URLs
[appletrailers] Add support
[addanime] improve
HTTPError is in urllib.error in Python 3, not in http.error