perf: unroll the result in perfrevset

With the new lazy revset implementation, we need to actually read all elements
to trigger all the computations. Otherwise a no-op if of course much faster than
the full work.

contrib/perf.py

@@ -335,7 +335,7 b' def perfrevset(ui, repo, expr, clear=Fal'
     def d():
         if clear:
             repo.invalidatevolatilesets()
-        repo.revs(expr)
+        for r in repo.revs(expr): pass
     timer(d)
 
 @command('perfvolatilesets')