rt: cleanup passing around of rust_env
adding uv::direct and beginning to work out tcp request case

lots of changes, here.. should've commited sooner.
- added uv::direct module that contains rust fns that map, neatly, to
the libuv c library as much as possible. they operate on ptrs to libuv
structs mapped in rust, as much as possible (there are some notable
exceptions). these uv::direct fns should only take inputs from rust and,
as neccesary, translate them into C-friendly types and then pass to the
C functions. We want to them to return ints, as the libuv functions do,
so we can start tracking status.
- the notable exceptions for structs above is due to ref gh-1402, which
prevents us from passing structs, by value, across the Rust<->C barrier
(they turn to garbage, pretty much). So in the cases where we get back
by-val structs from C (uv_buf_init(), uv_ip4_addr(), uv_err_t in callbacks)
, we're going to use *ctypes::void (or just errnum ints for uv_err_t) until
gh-1402 is resolved.
- using crust functions, in these uv::direct fns, for callbacks from libuv,
will eschew uv_err_t, if possible, in favor a struct int.. if at all
possible (probably isn't.. hm.. i know libuv wants to eventually move to
replace uv_err_t with an int, as well.. so hm).
- started flushing out a big, gnarly test case to exercise the tcp request
side of the uv::direct functions. I'm at the point where, after the
connection is established, we write to the stream... when the writing is
done, we will read from it, then tear the whole thing down.

overall, it turns out that doing "close to the metal" interaction with
c libraries is painful (and more chatty) when orchestrated from rust. My
understanding is that not much, at all, is written in this fashion in the
existant core/std codebase.. malloc'ing in C has been preferred, from what
I've gathered. So we're treading new ground, here!
some more stuff for libuv dealing w/ 1402.. should go away soon
changing ctypes:: to libc:: and impl of uv::direct::write()
impl of rustrt::rust_uv_write in c++ and whitespace cleanup
uv_write works, buffer passing still broke, can get sockaddr_in by val

.. but passing sockaddr_in by val back to C is broken, still passing by
ptr
.. the uv_write_cb is processed, but we have a status -1.. there is
also valgrind spew.. so buf passing is broken, still.
fixed passing in uv_buf_t ptr array in uv_write.. return status 0

ways to go, still..
fixed by-val from rust->c, use ++ sigil in native fn sig <-- NEVAR FORGET

have to use ++ sigil in rust-side extern fn decls in order to have rust
actually copy the struct, by value, onto the C stack. gotcha, indeed.

also adding a helper method to verify/remind how to pass a struct by-val
into C... check out the rust fn sig for rust_uv_ip4_test_verify_port_val()
for more infos
uv_buf_t's for uv_write() passed by-val .. no more mallocs or ptr cop-outs

so we're now adhering the libuv C api and passing structs by-val where
it is expected, instead of pulling pointer trickery (or worse having to
malloc structs in c++ to be passed back to rust and then into C again)
wired up uv_read_start and some helper funcs around uv_alloc_cb tasks
test_uv_tcp_request() fully working on linux

.. up next: windows!
.. impl'd uv::direct::read_stop() and uv::direct::close() to wrap things up
.. demonstrated sending data out of the uv_read_cb via a channel (which
we block on to recv all of it, complete w/ EOF notification) that is
read from after the loop exits.
.. helpers to read the guts of a uv_buf_t
.. an idea im kicking around: starting to pile up all of these hideous
data accessor functions in uv::direct .. I might make impl/iface pairs
for the various uv_* types that I'm using, in order to encapsulate those
data access functions and, perhaps, make the access look a little cleaner
(it still won't be straight field access, but it'll be a lot better)
.. formatting cleanup to satisfy make check
win32 tweaks
adding missing rust_uv_* entries in rustrt.def.in
massaging out struct-size differences between unix and win32
fixed unix uv struct err from prev commit, also starting uv docs
fixing libuv stuff in win32 (see #2064) .. pass sockaddr_in by-ref, for now
hello world test for a tcp server in libuv

.. im now going to refactor the tcp request and server tests to utilize
each other, so no more external network ugliness
refactored the tcp request and server tests into 1 test using loopback

..plus whitespace cleanup for make check
add low-level uv_async bindings for use in tcp test
add libuv error msg helpers.. flushing out windows tcp issue.