on unav upgrades, be more quiet by default and explain more with --verbose

closes #1772
unav upgrades: also print optimised-away upgrades
Fix my email address
Remove old stuff from the dev manual
Merge pull request #1792 from samoht/master

Fixes in dev manual
Don't set MANPATH on FreeBSD either (eg never set it on *BSD)

Closes #1786, thanks for reporting !
Add an opam file if absent on 'opam source'

this copies the existing opam file, but removes 'patches' and 'subst' files since
they have already been applied

Makes pinning the fetched source directly possible, including with 'source --pin'
Merge pull request #1790 from OCamlPro/unav-upgrades-verb

on unav upgrades, be more quiet by default and explain more with --verbose
Merge pull request #1793 from OCamlPro/bsd-manpath

Don't set MANPATH on FreeBSD either (eg never set it on *BSD)
Merge pull request #1794 from OCamlPro/source-pin

Add an opam file if absent on 'opam source'
Added proposal for depexts plugin architecture
git backend: be a little more quiet when fetching
Merge pull request #1804 from rdicosmo/depexts

Added proposal for depexts plugin architecture
Merge pull request #1806 from OCamlPro/git-quiet

git backend: be a little more quiet when fetching
Small fixes to the doc for 1.2
Merge pull request #1819 from OCamlPro/doc-for-1.2

Small fixes to the doc for 1.2
Refresh installation instructions for Fedora, CentOS, Ubuntu, Debian and OpenBSD

Also update for 1.2
doc: mention how to change pinning versions
Fixed bogus message when explicitely updating dev packages
Fix running from a non-existent dir