use node v0.8, fix 1st session, add pylint, misc

* use node v0.8
  - bump node to v0.8.26
  - use prebuilt node packages for nodeenv (faster setup!)
* fix for 1st session
  - add custom cloud9 server plugin to use memory-based sessions to avoid bug with file-based sessions (based on work by @shaohua)
  - add section to install our cloud9_ext plugins into cloud9
* add pylint
  - use python virtualenv v1.9.1 (combines with nodeenv)
* misc
  - check for dependencies early (curl and python)
  - minor fix for npm installs