test: raise fd limit for OSX select test

Fixes #42

PR-URL: https://github.com/libuv/libuv/pull/46
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
unix: remove overzealous assert in uv_read_stop

Also make it a noop if we weren't reading at all.
unix: reset the reading flag when a stream gets EOF
unix: stop reading if an error is produced

This aligns the behavior with Windows, where users don't need to
call `uv_read_stop` or `uv_close` if they get an error in the read
callback.