buffered transport broken when trying to re-open a formerly closed transport

TBufferedTransportImpl does not properly set and clear all member vars, which leads to all kinds of strange errors after reopening a formerly closed stream. Root cause is that InitBuffers must be called when Open-ing the transport again to get the internal interface pointers aligned again. If this is not done, any read/write may either fail straight away, or may produce errors that indicate an invalid underlying transport.