Rsync backend: allow remotes

this should allow all ssh remotes permitted by rsync. Still dubbed 'local' backend
in the code, and needs testing

use e.g. `user@host:dir/to/project/`. Don't forget the trailing slash.
Better error report on cyclic upgrade
Actions processing: finer handling of deps among versions

Fixes  #1778
Fixed exit code on upgrade resolution error
Merge pull request #1781 from OCamlPro/version-dep-cycles

Actions processing: finer handling of deps among versions
Merge remote-tracking branch 'OCamlPro/allow-ssh'

Conflicts:
	src/client/opamPinCommand.ml
	src/core/opamTypesBase.ml
	src/repositories/opamLocal.ml
Add travis ci on 4.02
Merge pull request #1679 from OCamlPro/travis-402

Add travis ci on 4.02
dev-manual: some fixes
Merge pull request #1783 from OCamlPro/dev-man-fix

dev-manual: some fixes
conflict messages: improvements

While we don't preserve exact version numbers in constraints when they don't match
an available package, this is an effort to preserve at least the comparison operator,
which is already much less confusing.

In particular, a bad equality constraint will show a not-so-nice but at least explicit
'package = <unavailable-version>'.

ref: #1787
unavailable because pinned: show version used
Merge pull request #1788 from OCamlPro/conflicts-msgs-cmp

Improvements to conflict messages
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'