resurrect compilers-to-packages script
Accept compiler definitions without upstream
More checks at resolution of the installation of base packages
Mark base packages are immovable to the solver
Add base packages to wish_install for the internal solver
Better error messages on conflicts involving base packages
Adjusting handling of base packages
Removed obsolete admin-script
Fixed the branch for cmd-engine
Fix tests for added compilers-packages precondition
Merge pull request #1889 from OCamlPro/compilers-packages-2

Allow handling of compilers within packages