moved some code around...
Game : define 'false' and 'true' constants.
Shared defs : create a fake 'bool' type (via typedef).
Client : check if mouse is "over the GUI", and if so then disable the
ability to select objects in the world.
drag_n_drop.txt : a bit more info.
Client : implemented the "ui_drop" command.
Game / inventory : implemented INV_CheckBeginDrag() which can test if
the user is pressing MB1 over a draggable object (in the world) and
begin the dragging process.  Object cannot be dropped yet :-)
Game : bit more work on drag-n-drop, added INV_CheckDrop() code.