Patch for Opcode.xs, for Perl <= 5.005.57

This patch does three things:
1) make code in a Safe:: partition think it's running in main:: (need for
   modules)
2) connect the _ in the partition to the global _ so it works right
3) set curstash to defstash like more recent Perls.



--- ext/Opcode/Opcode.xs-orig	Wed Jul 26 09:54:45 2000
+++ ext/Opcode/Opcode.xs	Wed Jul 26 09:54:17 2000
@@ -252,6 +252,14 @@
     save_hptr(&PL_defstash);		/* save current default stack	*/
     /* the assignment to global defstash changes our sense of 'main'	*/
     PL_defstash = gv_stashpv(Package, GV_ADDWARN); /* should exist already	*/
+    if (strNE(HvNAME(PL_defstash),"main")) {
+        Safefree(HvNAME(PL_defstash));         
+        HvNAME(PL_defstash) = savepv("main"); /* make it think it's in main:: */
+        hv_store(PL_defstash,"_",1,(SV *)PL_defgv,0);  /* connect _ to global */
+        SvREFCNT_inc((SV *)PL_defgv);  /* want to keep _ around! */
+    }
+    save_hptr(&PL_curstash);
+    PL_curstash = PL_defstash;
 
     /* defstash must itself contain a main:: so we'll add that now	*/
     /* take care with the ref counts (was cause of long standing bug)	*/