auto merge of #9235 : olsonjeffery/rust/newrt_file_io_1, r=thestinger

A quick rundown:

- added `file::{readdir, stat, mkdir, rmdir}`
- Added access-constrained versions of `FileStream`; `FileReader` and `FileWriter` respectively
- big rework in `uv::file` .. most actions are by-val-self methods on `FsRequest`; `FileDescriptor` has gone the way of the dinosaurs
- playing nice w/ homing IO (I just copied ecr's work, hehe), etc
- added `FileInfo` trait, with an impl for `Path`
  - wrapper for file-specific actions, with the file path always implied by self's value
  - has the means to create `FileReader` & `FileWriter` (this isn't exposed in the top-level free function API)
  - has "safe" wrappers for `stat()` that won't throw in the event of non-existence/error (in this case, I mean `is_file` and `exists`)
  - actions should fail if done on non-regular-files, as appropriate
- added `DirectoryInfo` trait, with an impl for `Path`
  - pretty much ditto above, but for directories
  - added `readdir` (!!) to iterate over entries in a dir as a `~[Path]` (this was *brutal* to get working)

...<del>and lots of other stuff</del>not really. Do your worst!

src/libstd/os.rs

@@ -196,16 +196,7 @@ pub fn env() -> ~[(~str,~str)] {
             if (ch as uint == 0) {
                 fail!("os::env() failure getting env string from OS: %s", os::last_os_error());
             }
-            let mut curr_ptr: uint = ch as uint;
-            let mut result = ~[];
-            while(*(curr_ptr as *libc::c_char) != 0 as libc::c_char) {
-                let env_pair = str::raw::from_c_str(
-                    curr_ptr as *libc::c_char);
-                result.push(env_pair);
-                curr_ptr +=
-                    libc::strlen(curr_ptr as *libc::c_char) as uint
-                    + 1;
-            }
+            let result = str::raw::from_c_multistring(ch as *libc::c_char, None);
             FreeEnvironmentStringsA(ch);
             result
         }