Merge input symbols: any device can have any input key.

- This reduces the number of types associated with input; adding a
   distinct input type doesn't introduce a whole new enumerated type
   and related functions.
 - Special handling for different devices is needed less often.  If you
   want to respond to an F1 press, simply check for KEY_F1; the device
   type doesn't really matter (though it'll usually be a keyboard).
 - This allows cleaner support for generalized USB devices.  While they're
   usually of the traditional classes (keyboard, joystick) with associated
   inputs, they don't have to be.
 - Forced casts between parallel types can be removed, and weakly-specified
   variables (ints instead of the enum type) can be fixed.

Some things that might have been merged havn't; for example, arrow keys
on a keyboard (KEY_UP) are still distinct from axes on a joystick (JOY_UP).
These may or may not be merged in the future.

Some were: removed PUMP_ symbols.  Treat them as generic buttons, and just
give them names with GetDeviceSpecificInputString.  It's not worth
introducing more special names for something only used in one place.

stepmania/src/InputFilter.cpp

@@ -140,7 +140,7 @@ void InputFilter::SetButtonComment( const DeviceInput &di, const CString &sComme
 void InputFilter::ResetDevice( InputDevice device )
 {
 	RageTimer now;
-	for( int button = 0; button < GetNumDeviceButtons(device); ++button )
+	FOREACH_ENUM2( DeviceButton, button )
 		ButtonPressed( DeviceInput(device, button, -1, now), false );
 }
 
@@ -173,7 +173,7 @@ void InputFilter::Update( float fDeltaTime )
 	 * things like "key pressed, key release, key repeat". */
 	LockMut(*queuemutex);
 
-	DeviceInput di( (InputDevice)0,0,1.0f,now);
+	DeviceInput di( (InputDevice)0,DeviceButton_Invalid,1.0f,now);
 
 	set<Button> Buttons( g_ButtonsToProcess );
 	FOREACHS( Button, Buttons, b )