Add benchmark for plain greenlet pools.

benchmarks/bench_pool.py

+# -*- coding: utf-8 -*-
+"""
+Benchmarks for greenlet pool.
+
+"""
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+
+import gevent.pool
+
+import bench_threadpool
+bench_threadpool.ThreadPool = gevent.pool.Pool
+
+if __name__ == '__main__':
+    bench_threadpool.main()