Non-daemon actions indirect through generated code.

Previously non-daemon actions were called directly by
user code, eg:

/* Non-generated */
int
guestfs_set_verbose (guestfs_h *g, int v)
{
  g->verbose = !!v;
  return 0;
}

This changes these actions so they go indirectly via
some generated code, eg:

/* Generated */
int guestfs_set_verbose (guestfs_h *g,
		int verbose)
{
  return guestfs__set_verbose (g, verbose);
}

/* Non-generated */
int
guestfs__set_verbose (guestfs_h *g, int v)
{
  g->verbose = !!v;
  return 0;
}

The aim is to have a place in the generated code where
we can add debug or tracing information for these non-
daemon calls.