Compile table traversals: next(), pairs(), BC_ISNEXT/BC_ITERN.

Sponsored by OpenResty Inc.

src/lj_asm_mips.h

@@ -2568,6 +2568,8 @@ static void asm_stack_restore(ASMState *as, SnapShot *snap)
       } else if ((sn & SNAP_SOFTFPNUM)) {
 	type = ra_alloc1(as, ref+1, rset_exclude(RSET_GPR, RID_BASE));
 #endif
+      } else if ((sn & SNAP_KEYINDEX)) {
+	type = ra_allock(as, (int32_t)LJ_KEYINDEX, allow);
       } else {
 	type = ra_allock(as, (int32_t)irt_toitype(ir->t), allow);
       }