Fix AHCIBufferAlign causing crashes on bare-metal.

Update 32-bit color graphics demo.
Add global Boolean to toggle window manager framebuffer writes.

src/Demo/Graphics/32BitColor.CC

@@ -11,7 +11,13 @@ I0 Color32Demo()
 	I64		i, j, x, y;
 	CBGR24	color;
 
-	while (TRUE)
+	"\nPress any key to exit demo.\n\n";
+
+	Sleep(500);
+
+	text.is_fb_busy = TRUE;
+
+	while (!CharScan)
 	{
 		x = FloorI64(RandU16 % GR_WIDTH, SQUARE_SIZE + SQUARE_GAP);
 		y = FloorI64(RandU16 % GR_WIDTH, SQUARE_SIZE + SQUARE_GAP);
@@ -21,8 +27,12 @@ I0 Color32Demo()
 			for (j = 0; j < SQUARE_SIZE; j++)
 				DrawPixel(x + i, y + j, color);
 
-		Busy(1000);
+		Sleep(100);
 	}
+
+	text.is_fb_busy = FALSE;
+	LFBFlush;
+
 }
 
 Color32Demo;

src/Kernel/BlkDev/DiskAHCI.CC

@@ -320,7 +320,7 @@ U8 *AHCIBufferAlign(CBlkDev *bd, U8 *user_buf, I64 buf_size, Bool write)
 //		"Aligning buffer under 32-bit range\n";
 
 		Free(bd->prd_buf);
-		bd->prd_buf = MAlloc(buf_size, Fs->code_heap);
+		bd->prd_buf = MAlloc(buf_size, zenith_task->code_heap);
 
 		Bts(&bd->flags, BDf_INTERNAL_BUF);
 

src/Kernel/KernelA.HH

@@ -4208,6 +4208,7 @@ public class CTextGlobals
 	U64 	*font, *aux_font, screen_size, buffer_size;
 	U8		*vga_alias;
 	U8		 border_chars[16];
+	Bool	 is_fb_busy;
 };
 
 #define FONT_WIDTH		8

src/Kernel/KeyDev.CC

@@ -190,6 +190,7 @@ U0 CtrlAltT(I64)
 U0 CtrlAltV(I64)
 {
 	LFBFlush;
+	text.is_fb_busy = FALSE;
 }
 
 U0 CtrlAltX(I64)

src/Zenith/Gr/GrScreen.CC

@@ -416,6 +416,9 @@ U0 GrUpdateScreen()
 {//Called by the Window Manager $LK,"HERE",A="FF:::/Zenith/WinMgr.CC,GrUpdateScreen"$, 30 times a second.
 	CDC *dc;
 
+	if (text.is_fb_busy)
+		return;
+
 	GrUpdateTextBG;
 	GrUpdateTextFG;
 	GrUpdateTasks;