[nailgun] Disable a debug mode for web.py

According to research of Lukasz Oles it will increase Nailgun's performance more than 40%.
For 2000 requests:
DEBUG OFF:
POST:
Time taken for tests: 14.147 seconds
PUT
Time taken for tests: 103.718 seconds

DEBUG ON:
POST
Time taken for tests: 50.347 seconds
PUT
Time taken for tests: 142.076 seconds