More NaN constant fixes.

This patch cleans up %loadi/wr regarding NaN values. It also
fixes the code generator to correctly output a NaN value as
a Cr<> constant.

tgt-vvp/vvp_scope.c

@@ -330,6 +330,10 @@ char* draw_Cr_to_string(double value)
 		  snprintf(tmp, sizeof(tmp), "Cr<m0g7fff>");
 	    return strdup(tmp);
       }
+      if (value != value) {
+	    snprintf(tmp, sizeof(tmp), "Cr<m1g3fff>");
+	    return strdup(tmp);
+      }
 
       int sign = 0;
       if (value < 0) {

vvp/vthread.cc

@@ -2663,7 +2663,7 @@ bool of_LOADI_WR(vthread_t thr, vvp_code_t cp)
 	    return true;
       }
 	// Detect NaN
-      if (exp==0x3fff && cp->number!=0) {
+      if (exp==0x3fff) {
 	    thr->words[idx].w_real = nan("");
 	    return true;
       }