hg serve: print a more useful error message if server can't start.

hg serve: print a more useful error message if server can't start.

--- a/mercurial/commands.py	Wed Aug 31 10:54:46 2005 -0700
+++ b/mercurial/commands.py	Wed Aug 31 11:19:20 2005 -0700
@@ -1386,7 +1386,10 @@
         if opts[o]:
             ui.setconfig("web", o, opts[o])
 
-    httpd = hgweb.create_server(repo)
+    try:
+        httpd = hgweb.create_server(repo)
+    except socket.error, inst:
+        raise util.Abort('cannot start server: ' + inst.args[1])
 
     if ui.verbose:
         addr, port = httpd.socket.getsockname()