if LBM files missing

Some folks (me!) deleted some of their LBM files decades ago. Game should not raise an exception if they are missing.
Handle ctrl-key
support strafing sideways movement

properly resubmitted, I hope.
Tank, turn turret with ctrl-click

Implements "strafe" move for tanks, in which ctrl-click turns the turret. The tank subsequently moves with the turret strafed.
Merge branch 'game_h_cpp_handle_ctrl_key'
add shift-to-run
Merge branch 'running'