Take a larger margin to prevent 'X' failures in smokes

I was able to get warnings on HP-UX 10.20 every 2nd to 3rd run
when reps was still 10000. With 15000 I didn't get a single warning

p4raw-id: //depot/perl@24964

diff --git a/t/op/rand.t b/t/op/rand.t
index 060d46a..eb29ff9 100755 (executable)
--- a/t/op/rand.t
+++ b/t/op/rand.t
@@ -27,7 +27,7 @@ require "test.pl";
 plan(tests => 8);
 
 
-my $reps = 10000;      # How many times to try rand each time.
+my $reps = 15000;      # How many times to try rand each time.
                        # May be changed, but should be over 500.
                        # The more the better! (But slower.)