Patch - check for msghdr.msg_control on Sparc-Solaris

[Warren_Baird at cimmetry.com]

> I think it would be better to do it using a technique similar to how it
> is done in scheduler/client.c on line 255:

Makes sense to me - it wasn't obvious that msg_control and msg_accrights are
always mutually exclusive, which is why I added a separate test...  But if we're
sure they are always mutally exclusive, this approach makes more sense...

Warren