Silence bogus warning when compiling with gcc46:

error: 'pos' may be used uninitialized in this function

Reviewed by:	cperciva
Approved by:	dim
MFC after:      3 days

usr.bin/bsdiff/bsdiff/bsdiff.c

@@ -272,7 +272,7 @@ int main(int argc,char *argv[])
 	/* Compute the differences, writing ctrl as we go */
 	if ((pfbz2 = BZ2_bzWriteOpen(&bz2err, pf, 9, 0, 0)) == NULL)
 		errx(1, "BZ2_bzWriteOpen, bz2err = %d", bz2err);
-	scan=0;len=0;
+	scan=0;len=0;pos=0;
 	lastscan=0;lastpos=0;lastoffset=0;
 	while(scan<newsize) {
 		oldscore=0;