adsense_injector 6.x-2.6-rc1

- completely upgrade and port to D6.
- version number starting with 2.6 (sync with D5).
- tested with adsense 6.x-1.0-beta3.
- renew hook_menu(). D6 coming with new implementation.
- watchdog() no longer require for t().
- hook_nodeapi() coming with new implementation for D6.
- split admin related hook_settings() to adsense_injector.admin.inc, as D6 style.
- retouch adsense_injector.info so group this module with Adsense.
- coding style cleanup.
- validate code with coder module.
- add more documentation.
- clean up license and developer information.
- document project owner and co-maintainer.
- remove legacy admin setting paypal banner.
- remove legacy _dbg().