[PATCH 1 of 5 STABLE v2] revsetbenchmarks: add an additional roots() benchmark

[Gregory Szorc]

# HG changeset patch
# User Gregory Szorc <gregory.szorc at gmail.com>
# Date 1410114802 25200
#      Sun Sep 07 11:33:22 2014 -0700
# Node ID eb5a18f2feaa61d48166198558035e82b8672a04
# Parent  188b8aa2120b03eead618ba150319074f4e3b42b
revsetbenchmarks: add an additional roots() benchmark

The existing roots(x - y) revset only considered the most recent 100
revisions. This was a good start. But expanding it to the full history
of the repository can dramatically increase execution time and thus
constitutes a useful benchmark.

diff --git a/contrib/revsetbenchmarks.txt b/contrib/revsetbenchmarks.txt
--- a/contrib/revsetbenchmarks.txt
+++ b/contrib/revsetbenchmarks.txt
@@ -22,4 +22,5 @@ draft()
 :10000 and draft()
 max(::(tip~20) - obsolete())
 roots((0:tip)::)
 (not public() - obsolete())
+roots((0::) - (0::tip))