With the fix in 77912a65e2, another bug
got visible: booleans are 32 bits, so if the intersection between the 2
bitmasks happened in higher bits, the return value would be truncated to
FALSE.
This actually made slider handles disappear, so it was pretty visible.
We need to use the allocated codepath if *any* argument is
allocated, not if one arg is not allocated.
This bug caused unnecessary calls to _gtk_bitmask_is_allocated,
as well as return completely wrong result if both bitmask are
allocated.
This does nothing but turn all GtkBitmask functions into static inline
functions that call the gtk_allocated_bitmask_*() equivalent.
The implementation of the static functions has also been put into a
private header, to not scare people who want to see how things are
implemented.
