`opam config env` now detects the current shell and outputs a sensible default if no override is provided.

This fixes the default installation on FreeBSD, which has csh as its default root shell.
Merge pull request #691 from avsm/config-env-autodetect

`opam config env` shell autodetection
Bump trunk to 1.1.0
Fix auto-completion scripts
Fix cygwin path (#598)
Use a tail-recursive version for {Set,Map}.fold

Fix should fix #696
Fix weird Not_found exception during 'opam upgrade'
Don't display auto-conflicts in the conflict explanation.

That's very spammy and not very useful as we cannot have two packages with the same version anyway.