This fixes the problem with OLPC touchscreen which does not generate
BTN_TOUCH (but reports that it has it), instead if generates
ABS_MT_TRACKING_ID=-1 when the finger is offscreen.

diff --git a/plugins/input-raw.c b/plugins/input-raw.c
index 10454da..e1c8c02 100644
--- a/plugins/input-raw.c
+++ b/plugins/input-raw.c
@@ -43,6 +43,8 @@
 #ifndef ABS_MT_POSITION_X
 # define ABS_MT_POSITION_X       0x35    /* Center X ellipse position */
 # define ABS_MT_POSITION_Y       0x36    /* Center Y ellipse position */
+# define ABS_MT_PRESSURE         0x3a    /* Pressure on contact area */
+# define ABS_MT_TRACKING_ID      0x39    /* Unique ID of initiated contact */
 #endif
 
 #include "tslib-private.h"
@@ -107,7 +109,9 @@ static int check_fd(struct tslib_input *i)
 	we set it to constant 255. It's still controlled by BTN_TOUCH/BTN_LEFT -
 	when not touched, the pressure is forced to 0. */
 
-	if (!(absbit[BIT_WORD(ABS_PRESSURE)] & BIT_MASK(ABS_PRESSURE))) {
+	if ( (absbit[BIT_WORD(ABS_PRESSURE)]    & BIT_MASK(ABS_PRESSURE))==0 && 
+	     (absbit[BIT_WORD(ABS_MT_PRESSURE)] & BIT_MASK(ABS_MT_PRESSURE))==0
+	   ) {
 		i->current_p = 255;
 
 		if ((ioctl(ts->fd, EVIOCGBIT(EV_KEY, sizeof(keybit)), keybit) < 0) ||
@@ -204,8 +208,12 @@ static int ts_input_read(struct tslib_module_info *inf,
 					i->current_y = ev.value;
 					break;
 				case ABS_PRESSURE:
+				case ABS_MT_PRESSURE:
 					i->current_p = ev.value;
 					break;
+				case ABS_MT_TRACKING_ID:
+					if (ev.value == -1) i->current_p=0;
+					break;
 				}
 				break;
 			}