Allow bitmap to be used in userspace

[mcimerman]

Hi,

I happen to need to use a bitmap for my project, but the one in HelenOS is
not available in libc, only for the kernel...

So I included it to be built in libc, but then userspace doesn't see <typedefs.h>
kernel header, which seems to not be needed by the bitmap.

Objections? Ok?

[vhotspur]

LGTM.

BTW, we have a nice dichotomy there as odict is also shared in kernel and userland and while it has guard _LIBC_ODICT_H_ it belongs to kernel_generic_adt documentation.