Added bignum test for +=.

Rev: src/testsuite.in:1.216

src/testsuite.in

-test_true([["$Id: testsuite.in,v 1.215 1999/10/30 23:23:59 hubbe Exp $"]])
+test_true([["$Id: testsuite.in,v 1.216 1999/10/31 14:58:27 grubba Exp $"]])
 
 cond([[all_constants()->_verify_internals]],
 [[
@@ -1406,6 +1406,10 @@ cond([[ sizeof( cpp("__AUTO_BIGNUM__")/"__AUTO_BIGNUM__" ) == 1 ]],
   test_eq("-2147483648", [[ (string)((-0x80000001) + 1) ]])
   test_false([[ objectp((-0x80000001) + 1) ]])
 
+  // - Add-eq.
+  test_eq([[ lambda() { int a=0x100000000; int b = a; a += 1; return b; }() ]],
+	  [[ 0x100000000 ]])
+
   // - Sub.
   test_eq("-2147483648", [[ (string)(-0x7fffffff - 1) ]])
   test_eq("-2147483649", [[ (string)(-0x80000000 - 1) ]])