Trivial Description
The scancode mapping for the "Print Screen" key is missing from the base keymap used by Guacamole's RDP support. This means that although Guacamole and usages of guacamole-common-js should correctly map the "Print Screen" key to its corresponding keysym (assuming the key is not intercepted by the OS), that keysym will not be transformed into the scancode required by RDP.
The necessary mapping needs to be added such that the correct scancode and flags are sent to the RDP server if the "Print Screen" keysym is received.