Merge pull request #733 from mirage/master

Fix Mirage compilation
Add missing files for extlib
Really fix extlib 1.5.4
Merge pull request #734 from mirage/master

more mirage build fixes for latest version
Merge branch 'master', remote-tracking branch 'upstream/master'
added package ocaml-ftp
Merge pull request #735 from blue-prawn/master

package for ocaml-ftp
The package "gsl-ocaml" does not exists anymore.
Merge pull request #737 from Chris00/master

The package "gsl-ocaml" does not exists anymore.
+cohttp.0.9.8, and constraints on older packages
+github.0.6.0