disable check on jump distance.  this might not
be a bootable fat or a pc.  see ecma-107 standard.
this is important for sd cards for digital cameras.

Reference: /n/sources/patch/applied/dossrvcamera
Date: Sat Oct  4 21:11:24 CES 2008
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/dossrv/dossubs.c	Sat Oct  4 21:10:17 2008
+++ /sys/src/cmd/dossrv/dossubs.c	Sat Oct  4 21:10:14 2008
@@ -21,9 +21,16 @@
 
 	/*
 	 * Check if the jump displacement (magic[1]) is too short for a FAT.
+	 * 
+	 * check now omitted due to digital cameras that use a 0 jump.
+	 * the ecma-107 standard says this is okay and that interoperable fat
+	 * implementations shouldn't assume this:
+	 * http://www.ecma-international.org/publications/files/ECMA-ST/Ecma-107.pdf, page 11
 	 */
-	if(buf[0] == 0xEB && buf[2] == 0x90 && buf[1] >= 0x30)
+	if(buf[0] == 0xEB && buf[2] == 0x90 /*&& buf[1] >= 0x30*/)
 		return 1;
+	if(chatty)
+		fprint(2, "bad sig %.2ux %.2ux %.2uxn", buf[0], buf[1], buf[2]);
 
 	return 0;
 }
@@ -101,6 +108,8 @@
 		bp->fatsize = GLONG(b32->fatsize32);
 		if(bp->fatsize == 0){
 			putsect(p);
+			if(chatty)
+				fprint(2, "fatsize 0\n");
 			return -1;
 		}
 		bp->dataaddr = bp->fataddr + bp->nfats*bp->fatsize;