The Guile process taking the role of PID 1 during Guix builds does not reap
zombie processes, which makes them continue responding to "kill -0".

--- a/src/testsuite/stop-server.sh	2015-02-05 11:24:00.535908842 +0100
+++ b/src/testsuite/stop-server.sh	2015-02-05 11:25:00.264351349 +0100
@@ -1,6 +1,21 @@
 #!/bin/sh
 # ngIRCd Test Suite
 
+process_is_alive(){
+    ! process_is_dead "$1" && ! process_is_undead "$1"
+}
+
+process_is_dead(){
+    ! kill -0 "$1"
+}
+
+process_is_undead(){
+    case $(ps -p "$1" -o state=) in
+        (Z*) true ;;
+        (*) false ;;
+    esac
+}
+
 [ -z "$srcdir" ] && srcdir=`dirname $0`
 
 # read in functions
@@ -24,7 +40,7 @@
 
 # waiting ...
 for i in 1 2 3 4 5; do
-  kill -0 $pid > /dev/null 2>&1; r=$?
+  process_is_alive $pid > /dev/null 2>&1; r=$?
   if [ $r -ne 0 ]; then
     echo " ok".
     exit 0
mit' value='switch'/></form></td></tr>
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<tr><td><span title='2018-11-14 21:34:08 +0100'>2018-11-14</span></td><td><a href='/guix/commit/nix/scripts?id=0fe1fba4af41f267c4bb2c006fb37f42422ab703'>daemon: Install 'authenticate' script under LIBEXECDIR/guix.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-12-31 11:18:30 +0100'>2017-12-31</span></td><td><a href='/guix/commit/nix/scripts?id=091191c3dcbfb9f01070d26bf15cb2c4dd07b1b5'>list-runtime-root: Fix off-by-one in 'strip-drop' call.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-11-26 15:58:33 +0100'>2017-11-26</span></td><td><a href='/guix/commit/nix/scripts?id=9b0713012905f3997d6fad201dba7c3d93b38b13'>list-runtime-roots: Ignore ESRCH while reading from /proc.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-11-12 23:53:12 +0100'>2017-11-12</span></td><td><a href='/guix/commit/nix/scripts?id=856b68bda959638201182304ded2759c7de5411b'>list-runtime-roots: Ignore PIDs we cannot access.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-11-12 22:42:17 +0100'>2017-11-12</span></td><td><a href='/guix/commit/nix/scripts?id=fb17a89912c2a3738dae716e30481c11e1c6f0ac'>list-runtime-roots: Canonicalize store items.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-11-12 22:42:17 +0100'>2017-11-12</span></td><td><a href='/guix/commit/nix/scripts?id=b8f59cdc20e9d83ce63523ef917e95fcee07f134'>list-runtime-roots: Do not use 'lsof'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-03-08 23:42:53 +0100'>2017-03-08</span></td><td><a href='/guix/commit/nix/scripts?id=ac9c1dc7bdf1a016fcd1989993999e4a32d0c885'>list-runtime-roots: Bufferize the lsof pipe.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2016-11-16 18:19:47 +0100'>2016-11-16</span></td><td><a href='/guix/commit/nix/scripts?id=94d92c7796a3dd50c27d532315f7d497ac99f08e'>daemon: Add "builtin:download" derivation builder.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>