$ pkg --julia=foobar --version
ERROR: LoadError: IOError: could not spawn `foobar -Cnative --compile=min -O0 -g1 /usr/local/bin/pkg --version`: no such file or directory (ENOENT)
Stacktrace:
[1] _spawn_primitive(::String, ::Cmd, ::Array{Any,1}) at ./process.jl:401
Print something nicer than