pipe_of_body should not close any handles

In keep alive mode connection is persistent. The closing logic is moved
to after the requests pipe has been cleared.

Fixes #105
Make Async SSL optional via optcomp (not plumbed through to build system yet)

This is unfortunately rather hard to do via OASIS, due to the tangling up
of OASIS, ocamlbuild, ocamlfind and optcomp...
Merge pull request #107 from rgrinberg/master

update .merlin
Merge pull request #106 from rgrinberg/body_post_bug

pipe_of_body should not close any handles
add sexplib/fieldslib to merlin
Make connection sexpable