t/lib-git-daemon: make sure to kill the 'git-daemon' process

After 'start_git_daemon' starts 'git daemon' (note the space in the
middle) in the background, it saves the background process' PID, so
the daemon can be stopped at the end of the test script.  However,
'git-daemon' is not a builtin but a dashed external command, which
means that the dashless 'git daemon' executes the dashed 'git-daemon'
command, and, consequently, the PID recorded is not the PID of the
"real" daemon process, but that of the main 'git' wrapper.  Now, if a
test script involving 'git daemon' is interrupted by ctrl-C, then only
the main 'git' process is stopped, but the real daemon process tends
to survive somehow, and keeps on running in the background
indefinitely, keeping the daemon's port to itself, and thus preventing
subsequent runs of the same test script.

Work this around by running 'git daemon' with the '--pidfile=...'
option to save the PID of the real daemon process, and kill that
process in 'stop_git_daemon' as well.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/lib-git-daemon.sh

@@ -31,6 +31,7 @@ fi
 test_set_port LIB_GIT_DAEMON_PORT
 
 GIT_DAEMON_PID=
+GIT_DAEMON_PIDFILE="$PWD"/daemon.pid
 GIT_DAEMON_DOCUMENT_ROOT_PATH="$PWD"/repo
 GIT_DAEMON_HOST_PORT=127.0.0.1:$LIB_GIT_DAEMON_PORT
 GIT_DAEMON_URL=git://$GIT_DAEMON_HOST_PORT
@@ -49,7 +50,7 @@ start_git_daemon() {
 	mkfifo git_daemon_output
 	${LIB_GIT_DAEMON_COMMAND:-git daemon} \
 		--listen=127.0.0.1 --port="$LIB_GIT_DAEMON_PORT" \
-		--reuseaddr --verbose \
+		--reuseaddr --verbose --pid-file="$GIT_DAEMON_PIDFILE" \
 		--base-path="$GIT_DAEMON_DOCUMENT_ROOT_PATH" \
 		"$@" "$GIT_DAEMON_DOCUMENT_ROOT_PATH" \
 		>&3 2>git_daemon_output &
@@ -88,8 +89,9 @@ stop_git_daemon() {
 	then
 		error "git daemon exited with status: $ret"
 	fi
+	kill "$(cat "$GIT_DAEMON_PIDFILE")" 2>/dev/null
 	GIT_DAEMON_PID=
-	rm -f git_daemon_output
+	rm -f git_daemon_output "$GIT_DAEMON_PIDFILE"
 }
 
 # A stripped-down version of a netcat client, that connects to a "host:port"