Minor python 2.4.3 compatibility issue

[paulfertser]

Hi,

Having Python 2.4.3 on a GNU/Linux system here, i had to make ``import
ctypes'' optional depending on os.name == 'nt' (it's not needed on a
sane system anyway) and also import email.utils didn't work before i
changed it to import email.Utils.

TIA :)

[phihag]

There's no official support for Python 2.4, but if these two imports is all what it prevents youtube-dl from running on 2.4, I don't see why it shouldn't be fixed.