[DGD] Error with 1.5.5

[Blain]

I triggered a segfault after compile_error and before runtime_error are
called in the driver object.  I created a bare bones implementation and
determined that the following does bug out.

[/driver.c]
void initialize() {
  call_out("load_foo");
}

void load_foo() {
  compile_object("/foo");
}

[/foo.c]
void foo() {
  test = ({});
}

Also, /auto.c and /auto.h are empty files.

With the variable test not being declared in foo.c, DGD segfaults.  The
error message given to compile_error is "undeclared variable test".