Call default mock method for virtual destructor

[malcolmdavey]

Make sure we copy and use the default mock destructor from the default virtual function table.

It seems it sets the default VTable up by default to call unmockedDtor(), but then makes a new VTable for the specific object but doesn't copy it across.

Seems to only be an issue on windows

A general work around is:

Fake(Dtor(mock));
// or When(Dtor(mock)).Do([](auto){} );

Another one for shared_ptr is this

shared_ptr ptr( &mock.get(), [](auto) {} );

Issue here:
#288

[coveralls]

Coverage remained the same at 99.925% when pulling fa2cd3d on iress:OSS-7-fix-virtual-destructor-windows into 78ca536 on eranpeer:master.

[FranckRJ]

Good catch, thanks.