as a publically callable routine. The device-callable routine will
be able to change the passthrough routine as M$ has two distinct
routines for aspi and ioctl.
We now are starting to have universal MMC routines. To do this we need
to have function pointers to the OS-specific MMC send/run command.
Expect some breakage. Down the line though this will increase code reuse,
reliabilty, and make the library more user-customizable.