Auto merge of #1070 - redox-os:relibc, r=alexcrichton
Auto merge of #1070 - redox-os:relibc, r=alexcrichton

Add additional Redox OS functions

This adds `chown`, `fchown`, `setenv`, and `unsetenv` to the `redox` module, and reorders the functions by name

rust-lang-nursery/libc,rust-lang/libc,rust-lang-nursery/libc,rust-lang/libc,rust-lang-nursery/libc,rust-lang/libc