Add test reproducing a bug in "hg serve -v"

tests/test-serve

@@ -0,0 +1,12 b''
+#!/bin/sh
+
+hg init test
+cd test
+
+echo % Without -v
+hg serve -a localhost -p 20063 -d --pid-file=hg.pid
+kill `cat hg.pid`
+
+echo % With -v
+hg serve -a localhost -p 20063 -d --pid-file=hg.pid -v
+kill `cat hg.pid`

tests/test-serve.out

@@ -0,0 +1,3 b''
+% Without -v
+% With -v
+listening at http://localhost:20063/