Bugfix: When receiving a frame with remote request bit set
not clearing m_nRtr until next data frame without request bit is
received. This lead to sending out all frames in between with
request bit set aswell. Fixed by extending sendMsgBuf to
INT8U sendMsgBuf(INT32U id, INT8U ext, INT8U rtr, INT8U len, INT8U *buf)
and setMsg to
INT8U setMsg(INT32U id, INT8U ext, INT8U len, INT8U rtr, INT8U *pData)
giving the possibillity to specify if request bit is set or not when
sending a message.

Feature: New function INT8U MCP_CAN::isRemoteRequest(void) added
to make it possible to check if the remote request bit was set on
the last received message.