Waf update

Created by: ederag

This is a PR for the waf update (issue #399 (closed)).

Need to (at least):

• add a license file to the waflib directory
• restore icon cache updates
• new waf dbus needs dbus-binding-tool ?
• installation instructions: documentation needs yelp
• restore help build
• make help installation optional (wip + need doc)
• update scrollkeeper ?
• change default prefix to usr
• do not use conf.define (get rid of compat15)
• more tests + instructions for other distros
• add uninstall instructions
• update NEWS