Links a _bstr_t wrapper to a BSTR.
A BSTR to be associated with, or assigned to, the _bstr_t variable.
If the _bstr_t was previously attached to another BSTR, the _bstr_t will clean up the BSTR resource, if no other _bstr_t variables are using the BSTR.
See _bstr_t::Assign for an example using Attach.
END Microsoft Specific