introducing flags_t

[Christoph Egger <Christoph_Egger%gmx.de@localhost>]

Hi!

In many places we use 'int' for flags.
Also in most places, the flag is checked this way:

   if (flags & FLAGX)
       do_something();

This is problematic when the top-most bit is used.

Per discussion with christos@ on source-changes-d@
I changed pmap to use u_int for the flags - almost.
I didn't change the ctor and dtor functions because that would imply
to change pool and pool_cache.

For better clarity and readability, I would like to use
a flags_t type.


Open questions:
- Where should it be defined? MI or MD?
- How should it be defined? Is 'typedef u_int flags_t;' ok?
- What about namespace pollution?


Christoph