`OwningHandle::new` should allow handle to propagate errors.

[jonhoo]

If the operation creating the handle fails for some reason, exposing that error is currently quite difficult. Could the signature of new perhaps be changed to

fn new<F, E>(o: O, f: F) -> Result<Self, E>
  where F: Fn(*const O::Target) -> Result<H, E> {}

[Kimundi]

Sounds reasonable! Instead of changing new, I added an try_new() constructor though.

Check it out on master and tell me if its the expected semantic. :)

[jonhoo]

try_new seems perfect!