Immediate HTTP(S) proxy (de)activation

Introduction of HttpProxy class which is based off of the SocksProxy class.
Allows for immediate HTTP(S) proxy activation and deactivation, as the configuration is changed.

src/conf.py

@@ -34,6 +34,7 @@ import time
 import socket
 
 from . import ircutils, registry, utils
+from .utils import minisix
 from .version import version
 from .i18n import PluginInternationalization
 _ = PluginInternationalization()
@@ -1169,8 +1170,33 @@ registerGlobalValue(supybot.protocols.http, 'peekSize',
     similar.  It'll give up after it reads this many bytes, even if it hasn't
     found what it was looking for.""")))
 
+class HttpProxy(registry.String):
+  """Value must be a valid hostname:port string."""
+  def setValue(self, v):
+    if minisix.PY2:
+      from urllib2 import build_opener, install_opener, ProxyHandler
+    else:
+      from urllib.request import build_opener, install_opener, ProxyHandler
+    proxies = {}
+    if v != "":
+      # TODO: improve checks
+      if ':' not in v:
+        self.error()
+      try:
+        int(v.rsplit(':', 1)[1])
+      except ValueError:
+        self.error()
+      proxies = {
+        'http': v,
+        'https': v
+        }
+    proxyHandler = ProxyHandler(proxies)
+    proxyOpenerDirector = build_opener(proxyHandler)
+    install_opener(proxyOpenerDirector)
+    super(HttpProxy, self).setValue(v)
+
 registerGlobalValue(supybot.protocols.http, 'proxy',
-    registry.String('', _("""Determines what proxy all HTTP requests should go
+    HttpProxy('', _("""Determines what proxy all HTTP requests should go
     through.  The value should be of the form 'host:port'.""")))
 utils.web.proxy = supybot.protocols.http.proxy