The normal xinit is racy because it doesn't use -displayfd. This
implements the bare minimum for testing purposes, using -displayfd to
sequence starting the client, and avoids adding yet another dependency
to the server.
v2: Fix asprintf error checks.
v3: Add error checking for fork(), clarify calloc() arg.
Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
