Convert PageAddItem into a macro to save a few cycles.

Nowadays this is just a backwards-compatibility wrapper around
PageAddItemExtended, so let's avoid the extra level of function call.
In addition, because pretty much all callers are passing constants
for the two bool arguments, compilers will be able to constant-fold
the conversion to a flags bitmask.

Discussion: <552.1473445163@sss.pgh.pa.us>