Added capability to bufinfo ioctl for marking bytes written and renamed its members.

Added capability to bufinfo ioctl for marking bytes written and renamed its members.
Changed prototype of RT version of comedi_request_irq to make dev_id a comedi_device* instead of a void*
since it is assumed to be so elsewhere in rt code.  Made comedi_switch_to_rt return an int
so it is able to return error on failure.  Fixes for overrun/underrun checking with dma in ni_mio_common.