stops the server from forking, unlinking, and opening most files

Generally a good idea, but this implementation is a hack
and should probably not be used by anybody.

Problems include:
 - this whole thing can also be solved from within racket
 - there is no guarantee that we intercept all security-breaking
   syscalls (the current implementation has *certainly* holes)
 - this only works on POSIX systems, probably even only on Linux
 - etc.