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 behaviour with 'opam pin edit'

Edit from a temp file rather than the real one, import file from
source even if it has errors (to let the user fix them), keep
the file formatting as-is when opam has no modifications to make

Fixes  #1613 (partially)
Closes  #1650
Remove need for 'opam update' just after 'opam repo add'
Improve `opam-admin findlib --infer`

You can use --install to have a more precise heuristic (still, we don't snapshot the filesystem yet)

You can use --orphans to get the list of install ocamlfind package minus the one we have already infered.
make cold: switch to released OCaml 4.02.0
Merge pull request #1669 from samoht/master

Improve `opam-admin findlib --infer`
Merge pull request #1670 from avsm/switch-to-cold-release

make cold: switch to released OCaml 4.02.0
Merge pull request #1666 from OCamlPro/small-fixes

A bunch of fixes on beta4, mostly UI
Improve default preferences to get the latest versions for new dependencies
Merge pull request #1668 from OCamlPro/no-add-update

Remove need for 'opam update' just after 'opam repo add'
Merge pull request #1667 from OCamlPro/better-pin-edit

Better behaviour with 'opam pin edit'
config report: some more solver info
Disabling disrupting 'cache of metadata' message
More tweaks to opam-admin findlib

the --install option will only try to install the packages if the findlib file
is empty. That will save lots of useless reinstallations.
Merge pull request #1677 from OCamlPro/solver-reports

Some more solver info on 'config report'
Be more precise when computing the orphans packages
`opam-admin findlib --orphans` should print nothing if there is no orphans

(not even an empty line)
Merge pull request #1675 from rdicosmo/updatepreferences

Improve default preferences to get the latest versions for new dependencies
Merge pull request #1678 from samoht/master

More tweaks to opam-admin findlib
Forward-compatibility

This enables a nicer warning on files advertising a newer opam-version than the exe,
enabling for those "permissive mode" that will parse what is compatible and silently
ignore what it doesn't understand (__the whole field__; granularity could be improved)

Still fails with newer MAJOR version number, or if $OPAMROOT/config advertises a newer
version

ref: #1662