tests/readlink.py

test-serve: make the 'listening at *' lines optional

The daemonized serve process doesn't print these lines out (see 448d0c452140).
I was able to get it to with the following hack:

 diff --git a/mercurial/win32.py b/mercurial/win32.py
 --- a/mercurial/win32.py
 +++ b/mercurial/win32.py
 @@ -418,6 +418,11 @@
          return str(ppid)

  def spawndetached(args):
 +
 +    import subprocess
 +    return subprocess.Popen(args, cwd=pycompat.getcwd(), env=encoding.environ,
 +                            creationflags=subprocess.CREATE_NEW_PROCESS_GROUP).pid
 +
      # No standard library function really spawns a fully detached
      # process under win32 because they allocate pipes or other objects
      # to handle standard streams communications. Passing these objects

However, MSYS translates --prefixes starting with '/' to 'C:/MinGW/msys/1.0',
which changes the output.  The output isn't so important that I want to spend a
bunch of time on this, and risk breaking some subtle behavior of `hg serve -d`
with the more complicated code.

#!/usr/bin/env python

from __future__ import absolute_import, print_function

import errno
import os
import sys

for f in sys.argv[1:]:
    try:
        print(f, '->', os.readlink(f))
    except OSError as err:
        if err.errno != errno.EINVAL:
            raise
        print(f, '->', f, 'not a symlink')

sys.exit(0)