sysimg.jl: delete bit-rotted `if false` debugging block.
Pkg2: some tweaks to status output.
Pkg2: checkout(pkg,[branch]) and release(pkg).

These are the names I settled on for checking out a branch version
of a package and then releasing the package back to management. I
started out having a `recur` option, but that turns out to be kind
of a nightmare to make work and is probably not needed that often.
Merge branch 'master' of github.com:JuliaLang/julia
Merge branch 'master' of github.com:JuliaLang/julia