Merge pull request #719 from samoht/master

Harder Better Safer 'opam update'
Compile with -g to get better issue reports
Merge branch 'master' of github.com:OCamlPro/opam
Fix doc target
Update API docs
Update man pages
Improve default dirnames in --help and man pages
Update tutorials
Proper implementation of pipe and compose operators

The previous 'pipe' was in fact 'compose' ...
Fix upgrade to 1.1 when some packages do not belong to any repository

Fix #725
Recreate the system compiler description during 1.0 => 1.1 upgrade
~/.opam/repo/index is now a map between *full* package to repo names

It used to be a map between package names to repo names, and this was very costly to know which repository to look for for a given package
Installed packages without any repository are not available
Speed-up 'opam list'
Always display the repository a package comes from with 'opam info'
Improve the error message in case of corrupted ~/.opam/repo/index
Remove dead-code (following 032951cca7270daca9bcc8f5b99e80ba111db02a)
Fix 'opam init'

We now do a full 'metada update' after the basic configuration files have been added.
Fix tests

'opam list -a' should show installable *and* installed packages. When an installed package does not have a repository, this set is different from installable only.
Update CHANGES