Generate the begin command once in a temporary buffer. Then,
depending on whether the command is to be written directly to the
hardware or to a secondary buffer, copy to command to the correct place.
Most occurances of U32 were converted to u32. These are cases where
the data represents something that will be written to the hardware.
Other cases were converted to 'unsigned int'.
U32 was the last type in xgi_types.h, so that file is removed.
Ian Romanick