updated proc/spawn syntax to nightly

This is building but failing tests with a linker error:

    Undefined symbols for architecture x86_64:
      "_eventfd", referenced from:
          EventFD::new::hf82ff66f9f3abc36Uaa in eventfd-16ec7bbf6c737d53.o
    ld: symbol(s) not found for architecture x86_64
    clang: error: linker command failed with exit code 1 (use -v to see invocation)

Using OS X 10.10 Yosemite with:

    transit% clang -v
    Apple LLVM version 6.0 (clang-600.0.56) (based on LLVM 3.5svn)
    Target: x86_64-apple-darwin14.0.0
    Thread model: posix

and:

    transit% rustc --version
    rustc 0.13.0-nightly (fea5aa656 2014-12-30 00:42:13 +0000)