add some explicit precompile statements for Pkg.status.

[KristofferC]

For some reason, these don't seem to "take" on our precompile workload.

Before:

julia> @time @eval Pkg.status()
0.470141 seconds (2.28 M allocations: 151.859 MiB, 2.91% gc time, 59.31% compilation time: 11% of which was recompilation)

After

julia> @time @eval Pkg.status()
  0.220179 seconds (1.69 M allocations: 122.680 MiB, 6.14% gc time, 25.84% compilation time: 74% of which was recompilation)