extend default thread pool workers of paster in pylons

add a option named threadpool_workers in server:main section in development.ini as below:

[server:main]
use = egg:Paste#http
host = 127.0.0.1
port = 5000
threadpool_workers = 20

then you will get this message from log:
11:09:33,678 INFO [paste.httpserver.ThreadPool] kill_hung_threads status: 20 threads (0 working, 20 idle, 0 starting) ave time N/A, max time 0.00sec, killed 0 workers