Switch to github hosting. Delete dead MASTER_SITES.
One tweak to a dependent (dose) due to a structure change.
Tweaks & ok sthen@ before 6.0 intervened
where needed.
The next step towards Ocaml 4.3.0.
Bulk build by sthen@ identified several laggards which are included here.
ok anil@ sthen@ so final 4.3.0 polishing can be done in-tree.