void CopyStdio(ICompiler comp, DataHash hc)
{
var stderrfile = outputCache.MakePath(hc.Hash, F_Stderr);
var stdoutfile = outputCache.MakePath(hc.Hash, F_Stdout);
comp.StdOutputCallback(File.ReadAllText(stdoutfile));
comp.StdErrorCallback(File.ReadAllText(stderrfile));
}