wendelin: Teach -dev build to dump all threads traceback on SIGUSR1

Via installing Products.signalstack

    https://pypi.python.org/pypi/Products.signalstack

/reviewed-by @Tyagov

software/wendelin/software-dev.cfg

@@ -7,7 +7,11 @@ parts -= wendelin.core
 parts += wendelin.core-dev
 
 
-# also tell erp5 to use -dev eggs instead of released ones
 [eggs]
+# tell erp5 to use -dev eggs instead of released ones
 eggs -= ${wendelin.core:egg}
 eggs += ${wendelin.core-dev:egg}
+
+# kill -USR1 <runzope-pid>    ->  traceback of all threads -> stdout
+#                                 ( logged to slappartX/.slappartX_zope-Y.log )
+        Products.signalstack