Missing beam.dll exports in R9C-2 for Windows

[James Hague]

All of the driver-related functions are not exported from beam.dll,
including driver_output.  This prevents dynamically loaded drivers from even
*loading* under Windows.

This is a showstopper for users of Wings, esdl, or any other application
making use of custom drivers.  I'd like to see a new beam.dll for R9C-2
posted as soon as possible.

James