clang++ using -stdlib=libc++ defines const_reference as a class,
to map boolean vectors onto a bit set. Because swig does
not "see" the type as "const &" it generates incorrect code for this case,
generating a declaration like:
const_reference result;
When const_reference is a typedef to 'bool' as is the case with stdlibc++
this works. When this is actually a constant reference, this is clearly
invalid since it is not initialized. For libc++, this is a class
which cannot be default constructed, resulting in an error. The fix
is to explicitly define the various accessor extensions as having a
bool return type for this specialization.
