[patch] build shark as an additional vm, if the default vm is zero

[Edward Nevill]

>this allows you to configure with --additional-vms=shark, when the default vm is 
>zero. it's useful if you build packages with shark support which shouldn't mess 
>around with you default configuration. You can start with -Xint, but I didn't 
>see anything how to make this the default, and for now I'd like to give 
>developers the chance to test with shark without interfering with the default vm.

Looks good to me.

Ed.