Fix exit status of xzgrep when grepping binary files.

When grepping binary files, grep may exit before it has
read all the input. In this case, gzip -q returns 2 (eating
SIGPIPE), but xz and bzip2 show SIGPIPE as the exit status
(e.g. 141). This causes wrong exit status when grepping
xz- or bzip2-compressed binary files.

The fix checks for the special exit status that indicates SIGPIPE.
It uses kill -l which should be supported everywhere since it
is in both SUSv2 (1997) and POSIX.1-2008.

Thanks to James Buren for the bug report.

src/scripts/xzgrep.in

@@ -195,7 +195,8 @@ for i; do
     fi >&3 5>&-
   )
   r=$?
-  test "$xz_status" -eq 0 || test "$xz_status" -eq 2 || r=2
+  test "$xz_status" -eq 0 || test "$xz_status" -eq 2 \
+      || test "$(kill -l "$xz_status" 2> /dev/null)" = "PIPE" || r=2
   test $res -lt $r && res=$r
 done
 exit $res