Replace non-portable (on MacOS X at least) `sed` with a `grep -v`

This fixes `oasis setup` and compiling the development version of Lwt
for me on MacOS X 10.8.
OCaml 4.01.0dev has a Unix.O_CLOEXEC flag, so add this to Lwt_unix too.

This was added quite recently in ocaml/ocaml@2207c45056e69d1ea5
Lwt_unix: fix grammar/spelling in module overview
Lwt_unix.sleep: fix documentation grammar
Lwt_unix.yield: fix documentation grammar
Lwt_unix.auto_yield: fix documentation grammar
Lwt_unix.timeout: fix documentation grammar
Lwt_unix.on_signal: fix documentation grammar
Lwt_unix.accept_n: fix doc grammar/typos
Lwt_unix.readdir: fix wrong reference to Unix
Merge pull request #3 from agarwal/documentation

Documentation
Merge pull request #1 from avsm/more-portable-setup

Replace non-portable (on MacOS X at least) `sed` with a `grep -v`
[fix] ev_timer_init last arg is the repeat delay, not a boolean flag
Merge pull request #2 from avsm/fix-4.01-build-with-cloexec

OCaml 4.01.0dev has a Unix.O_CLOEXEC flag, so add this to Lwt_unix too.
add lwt-log lib (unix free) rev1
better interface for Lwt_log_rules

better interface for Lwt_log_rules
[typo] Bool_val to Double_val
Merge pull request #4 from williamleferrand/master

[fix] ev_timer_init last arg is the repeat delay, not a boolean flag
update doc wrt previous changes
typo