chgserver: resolve relative path before sending via system channel

The chgserver may have a different cwd from the client because of the side
effect of "--cwd" and other possible os.chdir done by extensions. Therefore
relative paths can be misunderstood by the client.

This patch solves it by expanding relative cwd path to absolute one before
sending them via the 'S' channel. It can help chg to pass a testcase in
test-alias.t later.

hgext/chgserver.py

@@ -314,7 +314,7 b' class channeledsystem(object):'
         self.channel = channel
 
     def __call__(self, cmd, environ, cwd):
-        args = [util.quotecommand(cmd), cwd or '.']
+        args = [util.quotecommand(cmd), os.path.abspath(cwd or '.')]
         args.extend('%s=%s' % (k, v) for k, v in environ.iteritems())
         data = '\0'.join(args)
         self.out.write(struct.pack('>cI', self.channel, len(data)))