Fix upgrade to 1.1 when the current compiler is the system one
Fix pretty-printing and parsing of pinned package
Add OpamPackage.is_pinned
Improve the message when installing a pinned package
Clean-up pin-related functions in OpamState
Add OpamPath.Switch.{descr,files} definitions to deal with complete overlays
Add more overlay helper functions to OpamState
Propagate the change in the overlay API to OpamPinCommand

Now, everytime we pin a package, we create a new complete overlay for the package: the OPAM, descr and additional files are copied from the latest available package with the same name, and a crafter URL file is added.
Improve the display of action when a package is pinned
Improve global consistency checks to take pinned packages into account
Fix pinned package overlays when upgrading from 1.0 to 1.1
Fix reinstallation of pinned packages
Fix update of pinned packages