Bug with TVirtualCollectionProxy and std::bitset

Difficulties accessing a std::bitset through TVirtualCollectionProxy, in particular reading data via the `At` method and interpreting it via `AsString()` of underlying data type.
The `Size()` also gives a wrong result for bitset.

The attached source code demonstrates the problems.

It should be run like this:

.L testcase.C+

testvector()

testbitset()

The same code is executed for a kSTLvector proxy (works ok) and for a kSTLbitset proxy (does not work).