Privatize appropriate struct fields in core and std

[bstrie]

< bstrie> pcwalton: do you know why priv is commented out on this line in
          std::future? 
          https://github.com/mozilla/rust/blob/master/src/libstd/future.rs#L30
<@brson> bstrie: because the priv keyword wasn't supported there at the
         time. it's a reminder that that field should be 'priv'
< bstrie> ok, so that should be changed then
<@brson> yes

Find all priv fields of this type and uncomment them. Should perhaps also go through the rest of the libraries and stick priv qualifiers wherever their use may have been overlooked.

[wting]

Trying to add priv to this line causes the error: error: unmatched visibility. I'm not sure what that means though...

Also, how would we know where it's appropriate to add priv qualifiers?

Edit: Never mind about the 1st point:

< strcat> wting: I don't think you can make the extern mod stuff not get re-exported atm

[catamorphism]

(bug triage) Still an issue; good easy starter project.

[pnkfelix]

triage, email from 2013-09-09. Nothing to add.

[brson]

This is done I think thanks to @reedlepee123.