ocaml-ssl: Update to 0.4.7 and switch to GitHub mirror

Signed-off-by: Euan Harris <euan.harris@citrix.com>
optcomp: Update to 1.6 and get sources from GitHub.

Signed-off-by: Euan Harris <euan.harris@citrix.com>
ocaml-zed: Update to 1.6 and get sources from GitHub

Signed-off-by: Euan Harris <euan.harris@citrix.com>
ocaml-text: Update to 0.7.1 and get sources from GitHub.

Signed-off-by: Euan Harris <euan.harris@citrix.com>
downloader: Don't verify SSL certificates for forge.ocamlcore.org

OCaml Forge's SSL certificate has expired.

Signed-off-by: Euan Harris <euan.harris@citrix.com>
Merge pull request #540 from euanh/github-mirrors

Switch from OcamlForge to GitHub, where possible