Instead of using a special bitfield use a compound of boolean
values for the generic page attributes. To reduce copy overhead,
change the corresponding functions, where Page_flags are used as
arguments, to use references.
Previously, if two ID allocators for different kernel objects had the
same size, the kernel-object framework managed both objects types
through the same allocator instance. This is caused by the use of
unsynchronized singletons in the accessor functions and can be avoided
by creating new types through inheritance instead of using typedefs.
Anyways, this fix is a little bit ugly and should replaced by avoiding
the use of unsynchronized singletons in the future.
fix#906
