Replace _make_safe by functools.wraps

[Elrond]

To make decorators nicer, MediaGoblin has a tiny tool called _make_safe() in decorators.py.

But what this helper tool does, is actually in the standard library!

It's called functools.update_wrapper (1)
There's also a nicer version called functools.wraps (2)

So replace all instances of _make_safe by one of those two.

(1) ​http://docs.python.org/library/functools#functools.updat_wrapper
(2) ​http://docs.python.org/library/functools#functools.wraps

[Jakob Kramer]

​Patch

[Christopher Allan Webber]

Looks good. I merged it! Thank you! :)