[Omake] Command syntax

[Benjamin Pierce]

> P.S. BTW, in 0.9.8 we made it explicit when a shell command is  
> evaluated internally:
>
> *** omake: reading OMakefiles
> *** omake: finished reading OMakefiles (0.3 sec)
> - build . foobar
> + Shell.chmod(-w foo)
> *** omake error:
>    Lm_arg.BogusArg("No such option: -w")

Much better!

     - B