output error message if we can't start a php server

Co-authored-by: Tim Düsterhus <timwolla@googlemail.com>

Author: dbu

bin/http_test_server

@@ -8,4 +8,9 @@ if [ -f "$DIR/../autoload.php" ]; then
 # Development
 elif [ -f "$DIR/../vendor/autoload.php" ]; then
     php -S 127.0.0.1:10000 -t "$DIR/../fixture"
+# Not working, e.g. windows which does not do symlinks
+else
+    echo "*** Can't find the fixture folder ***" >&2
+    echo "Please write your own way to start a PHP web server on port 10000 for the 'fixture' directory." >&2
+    exit 1
 fi