Add {get,set}thrname(2) for putting thread names in the kernel and

Add {get,set}thrname(2) for putting thread names in the kernel and
exposed in a new field returned by sysctl(KERN_PROC).  Update
pthread_{get,set}_name_np(3) to use the syscalls.  Show them, when
set, in ps -H and top -H output.

libc and libpthread minor bumps

ok mpi@, mvs@, deraadt@