[VERSION 2.10] - Multiple disk drives supported.

[VERSION 2.11] - Corrects formatting problem, "bad parameter," for DOS versions
                 less than 4.0.

[VERSION 2.12] - Gives "WARNING!" rather than error when user attempts to make
                 the default drive equal to either the SOURCE or TARGET drive.

[VERSION 2.20] - XMS memory support!

[VERSION 2.21] - Fixed bug that occurred when copying multiple, different disks.
                 The first disk always copied fine, but the program didn't
                 reliably free up XMS and RAM prior to starting another disk.