Buffer objects would return the read or write buffer for a wrapped object when

Buffer objects would return the read or write buffer for a wrapped object when
the char buffer was requested.  Now it actually returns the char buffer if
available or raises a TypeError if it isn't (as is raised for the other buffer
types if they are not present but requested).

Not a backport candidate since it does change semantics of the buffer object
(although it could be argued this is enough of a bug to bother backporting).