+ move MKGet()/MKFree() into the only file that can use them.

+ remove useless wrappers around bcmp(), bcopy(), bzero().

The code assumes that bcmp() returns 0 if the size is 0, but
this is true for both the libc and the libkern versions.

+ nuke Bcmp, Bzero, Bcopy from radix.h now that nobody uses them anymore.