Added a workaround for umk3059gre and umk3137b5gre.

It's a hack, but a well-understood and clearly documented one.
Maybe smf can fix it for real in the distant future.

src/mame/machine/midwunit.c

@@ -400,6 +400,33 @@ static void init_wunit_generic(void)
 
 /********************** Mortal Kombat 3 **********************/
 
+static UINT16 *umk3_palette;
+
+static WRITE16_HANDLER( umk3_palette_hack_w )
+{
+	/*
+		UMK3 uses a circular buffer to hold pending palette changes; the buffer holds 17 entries
+	    total, and the buffer is processed/cleared during the video interrupt. Most of the time,
+	    17 entries is enough. However, when characters are unlocked, or a number of characters are 
+	    being displayed, the circular buffer sometimes wraps, losing the first 17 palette changes.
+	    
+	    This bug manifests itself on a real PCB, but only rarely; whereas in MAME, it manifests
+	    itself very frequently. This is due to the fact that the instruction timing for the TMS34010
+	    is optimistic and assumes that the instruction cache is always fully populated. Without
+	    full cache level emulation of the chip, there is no hope of fixing this issue without a
+	    hack.
+	    
+	    Thus, the hack. To slow down the CPU when it is adding palette entries to the list, we
+	    install this write handler on the memory locations where the start/end circular buffer
+	    pointers live. Each time they are written to, we penalize the main CPU a number of cycles.
+	    Although not realistic, this is sufficient to reduce the frequency of incorrect colors
+	    without significantly impacting the rest of the system.
+	*/
+	COMBINE_DATA(&umk3_palette[offset]);
+	activecpu_adjust_icount(-100);
+/*	printf("in=%04X%04X  out=%04X%04X\n", umk3_palette[3], umk3_palette[2], umk3_palette[1], umk3_palette[0]); */
+}
+
 static void init_mk3_common(void)
 {
 	/* common init */
@@ -427,11 +454,13 @@ DRIVER_INIT( mk3r10 )
 DRIVER_INIT( umk3 )
 {
 	init_mk3_common();
+	umk3_palette = memory_install_write16_handler(0, ADDRESS_SPACE_PROGRAM, 0x0106a060, 0x0106a09f, 0, 0, umk3_palette_hack_w);
 }
 
 DRIVER_INIT( umk3r11 )
 {
 	init_mk3_common();
+	umk3_palette = memory_install_write16_handler(0, ADDRESS_SPACE_PROGRAM, 0x0106a060, 0x0106a09f, 0, 0, umk3_palette_hack_w);
 }