CHANGES:

- Added new form_* functions to common.inc, used for building
  forms: it should improve 'stability' (no form typos, every-
  thing properly escaped/unescaped) and should help providing
  a very consistent user interface (wrt forms).

- Adjusted node.module to use the new form functions.
  (Can be used as an example.)

- Adjusted book.module to use the new form functions.
  (Can be used as an example.)

- Merged function.inc into common.inc!

- Slowly removing all global $status and $rstatus variables:
  use node_status() instead.

TODO:

- Apart from implementing the permission system, I'll spend
  some time updating most modules today and tomorrow to use
  the new form functions.