Migrate starsha to <base/subprocess.h>

This migrates starsha to use \<base/subprocess.h> and \<strm/> for doing I/O to subprcesses it starts (Individual compilation jobs, running various tools). 

There is also some general cleanup:

 - Moving users of \<starsha/runner> to use \<base/subprocess>
 - Making tests not print to stderr (The previous runner didn't do what it said)
 - Make bootstrap.sh a little nicer
 - Make PrintCmds no longer a global / pipe it through properly.

@JasonL9000: Look good to you?