Use an in-memory ccache to silence a compiler warning, for RT#6414.

diff -up krb5-1.8/src/slave/kprop.c.kprop-mktemp krb5-1.8/src/slave/kprop.c
--- krb5-1.8/src/slave/kprop.c.kprop-mktemp	2009-11-06 18:29:12.000000000 -0500
+++ krb5-1.8/src/slave/kprop.c	2010-03-05 10:59:06.000000000 -0500
@@ -202,9 +202,8 @@ void PRS(argc, argv)
 void get_tickets(context)
     krb5_context context;
 {
-    char   buf[BUFSIZ];
+    char buf[] = "MEMORY:_kproptkt";
     krb5_error_code retval;
-    static char tkstring[] = "/tmp/kproptktXXXXXX";
     krb5_keytab keytab = NULL;
 
     /*
@@ -229,11 +228,8 @@ void get_tickets(context)
 #endif
 
     /*
-     * Initialize cache file which we're going to be using
+     * Initialize an in-memory cache for temporary use
      */
-    (void) mktemp(tkstring);
-    snprintf(buf, sizeof(buf), "FILE:%s", tkstring);
-
     retval = krb5_cc_resolve(context, buf, &ccache);
     if (retval) {
         com_err(progname, retval, "while opening credential cache %s",