Added our copyright statements to some of the files in the top bsd/
directory, and in bsd/porting.

I only added our copyright to files which were completely by us - I did
not attempt to hunt which bsd or solaris files we modified to add our
copyright to them, I don't think this is important (or, we can do this
later).

I also found one header file (uma_stub.h) that had large chunks copied from
freebsd, so I added both the freebsd copyright and ours.