Support for custom 503 responses

Added support for a custom 503 (temporary maintenance) page based upon
the DISABLED file in an app folder

applications/examples/static/503.html

@@ -0,0 +1 @@
+<html><body><h1>Temporarily down for maintenance</h1></body></html>

applications/welcome/static/503.html

@@ -0,0 +1 @@
+<html><body><h1>Temporarily down for maintenance</h1></body></html>

gluon/main.py

@@ -25,7 +25,7 @@ import socket
 import random
 import string
 
-from gluon._compat import Cookie, urllib2
+from pydal._compat import Cookie, urllib2
 #from thread import allocate_lock
 
 from gluon.fileutils import abspath, write_file
@@ -390,7 +390,11 @@ def wsgibase(environ, responder):
                                    % 'invalid request',
                                    web2py_error='invalid application')
                 elif not request.is_local and exists(disabled):
-                    raise HTTP(503, "<html><body><h1>Temporarily down for maintenance</h1></body></html>")
+                    if os.path.exists(os.path.join(request.folder,'static','503.html')):
+                        import urllib
+                        raise HTTP(503, urllib.urlopen(os.path.join(request.folder,'static','503.html')).read())
+                    else:
+                        raise HTTP(503, "<html><body><h1>Temporarily down for maintenance</h1></body></html>")
 
                 # ##################################################
                 # build missing folders