windows: map WSANO_DATA to UV_ENOENT

This improves uv_getaddrinfo error reporting.

unix: add relaxed accept() setting

Mitigates unfair scheduling in multi-process setups that share a single listen
socket across multiple processes.

windows: invalid stdio handles should be INVALID_HANDLE_VALUE and not NULL

windows: only allow opening directories for reading

This is closer to the Posix model.

windows: initialize uv_fs_t.path to NULL

This shouldn't be necessary, but node v0.8 relies on it.

windows/uv_spawn: ignore errors when duplicating fd 0-2 fails

Hopefully this fixes joyent/node#3779.

windows: fix the MinGW build

windows: improve uv_fs_unlink

* It's now more efficient, the file is not opened twice.
* It no longer allows deletion of non-symlink directory reparse points.

windows: fix regression in uv_fs_link

Old and new path were accidentally reversed.

sunos: workaround OS bug to prevent fs.watch() from spinning

This is a back-port of commit cfb06db from the master branch.

Fixes joyent/node#3768.

sunos: workaround OS bug to prevent fs.watch() from spinning

Fixes joyent/node#3768.

doc: add 'Intro to libuv' link to README

Add a link to 'An Introduction to libuv' to the documentation section of
README.md. Format the section as a bullet list.

include: move ssize_t workaround to uv-win.h

windows: fix memory leaks in fs

Also clean up the code in various ways.

include: move ssize_t workaround to uv-win.h

Avoid compiler warning

Merge branch 'v0.8'

linux: fix 'two watchers, one path' segfault

Problem: registering two uv_fs_event_t watchers for the same path, then closing
them, caused a segmentation fault. While active, the watchers

linux: fix 'two watchers, one path' segfault

Problem: registering two uv_fs_event_t watchers for the same path, then closing
them, caused a segmentation fault. While active, the watchers didn't work right
either, only one would receive events.

Cause: each watcher has a wd (watch descriptor) that's used as its key in a
binary tree. When you call inotify_watch_add() twice with the same path, the
second call doesn't return a new wd - it returns the existing one. That in turn
resulted in the first handle getting ousted from the binary tree, leaving
dangling pointers.

This commit addresses that by storing the watchers in a queue and storing the
queue in the binary tree instead of storing the watchers directly in the tree.

Fixes joyent/node#3789.

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test: add uv_loop_t to benchmark-sizes.c

test: add uv_fs_event_t to benchmark-sizes.c

test: add failing fs_event test

Watches the same file twice. Fails on Linux with a segmentation fault.

include: update confusing uv_write comment

Raise UV_ECANCELED on premature close.

Set the error code to the more appropriate UV_ECANCELED instead of UV_EINTR
when the handle is closed and there are in-flight requests.

include: update uv_close documentation

unix: don't abort() when trylock functions return EBUSY

Fixes #500.