These functions were doing exactly the same thing for range allocation, so
share that code in an allocate_range() helper.
Region allocation will now also fail if range allocation fails, which means
that mmap() can actually fail without falling apart. Exciting times!
Make the Socket functions take a FileDescriptor& rather than a socket role
throughout the code. Also change threads to block on a FileDescriptor,
rather than either an fd index or a Socket.
Calling systrace(pid) gives you a file descriptor with a stream of the
syscalls made by a peer process. The process must be owned by the same
UID who calls systrace(). :^)
