std/rt: in-progress file io work

std: remove unneeded field from RequestData struct

std: rt::uv::file - map us_fs_stat & start refactoring calls into FsRequest

std: stubbing out stat calls from the top-down into uvio

std: us_fs_* operations are now by-val self methods on FsRequest

std: post-rebase cleanup

std: add uv_fs_mkdir|rmdir + tests & minor test cleanup in rt::uv::file

WORKING: fleshing out FileStat and FileInfo + tests

std: reverting test files..

refactoring back and cleanup...
merge cleanup
std: adding file::{stat,mkdir,rmdir}, FileInfo and FileReader/FileWriter

add ignores for win32 tests on previous file io stuff...
std: win32 os::env() str parsing to str::raw::from_c_multistring + test
std: clean up Dir/FileInfo inheritence and flesh out Dir Info
std: more work on from_c_multistring.. let it take an optional len param
std: expose more stat info
std: bind uv_fs_readdir(), flesh out DirectoryInfo and docs/cleanup
std: unignore some file io tests that work on windows, now
std: correctly pass STDOUT in to naive_print test fn
std: generlize & move io::file::suppressed_stat to io::ignore_io_error
std: remove impl'd/commented-out fstat signatures
std: FsRequest.req_boilerplate() be &mut self
std: lots of docs for std::rt::io::file

i hope they don't bitrot
std: minor cleanup in some io_error descs in io::file
std: docstring fixes in io::file
std: merge conflict cleanup from std::str
The purpose of these headers is to fix issues with mingw v4.0, as described in #9246.

This works by adding this directory to GCC include search path before mingw system headers directories,
so we can intercept their inclusions and add missing definitions without having to modify files in mingw/include.
Disabled tests which now fail on Windows+mingw4.0 due to GCC 4.8 ABI change (#9205).
These really should have been marked xfail-win32, but that doesn't exist, so xfail-fast it is.
std: remove RtioStream