Fix security issue in _prolog_error().

Fix security issue caused by insecure file path handling triggered by
the failure of a Prolog script. To exploit this a user needs to
anticipate or cause the Prolog to fail for their job.

(This commit is slightly different from the fix to the 15.08 branch.)

CVE-2016-10030.
_destroy_env(char **env)
{
	int i=0;

	if (env) {
		for(i=0; env[i]; i++) {
			xfree(env[i]);
		}
		xfree(env);
	}

	return;
}

_destroy_env(char **env)
{
	int i=0;

	if (env) {
		for(i=0; env[i]; i++) {
			xfree(env[i]);
		}
		xfree(env);
	}

	return;
}
