Yes, for some reason it is linked explicitly specifying minor version. To run it, do the following:

• run 'locate libGL' to see where do you have libGL.so installed
• if you have multiple libGL.so libraries, choose the one used by your current driver (e.g., if you have one in /usr/lib/mesa and another in /usr/lib/nvidia-current, and you are currently using nvidia driver, use that in /usr/lib/nvidia...)
• create the symbolic link 'libGL.so.1.2' in the same directory 'libGL.so' lives. For example, 'cd /usr/lib/nvidia-current', 'ln -sT libGL.so.195.36.24 libGL.so.1.2'
• use the following script to run the game (you may need to modify the library paths in the script):

     #!/bin/sh
    LD_LIBRARY_PATH=/usr/lib/nvidia-current:$LD_LIBRARY_PATH
    export LD_LIBRARY_PATH
    ./PhytaWindowed800x600

There is always more to discover in nethack, and always another strange manner in which to die…

Question though: what are the must-have mods/extensions for this game?

Cool, that's a lot clearer :)