Web: Disable the fetch sandbox on Python versions with the _MAXHEADERS fix.

Partial fix to GH-1271.

plugins/Web/plugin.py

@@ -46,9 +46,11 @@ _ = PluginInternationalization('Web')
 if minisix.PY3:
     from html.parser import HTMLParser
     from html.entities import entitydefs
+    import http.client as http_client
 else:
     from HTMLParser import HTMLParser
     from htmlentitydefs import entitydefs
+    import httplib as http_client
 
 class Title(utils.web.HtmlToText):
     entitydefs = entitydefs.copy()
@@ -90,6 +92,21 @@ class DelayedIrc:
         assert name not in ('reply', 'error', '_irc', '_msg', '_replies')
         return getattr(self._irc, name)
 
+if hasattr(http_client, '_MAXHEADERS'):
+    def fetch_sandbox(f):
+        """Runs a command in a forked process with limited memory resources
+        to prevent memory bomb caused by specially crafted http responses.
+
+        On CPython versions with support for limiting the number of headers,
+        this is the identity function"""
+        return f
+else:
+    # For the following CPython versions (as well as the matching Pypy
+    # versions):
+    # * 2.6 before 2.6.9
+    # * 2.7 before 2.7.9
+    # * 3.2 before 3.2.6
+    # * 3.3 before 3.3.3
     def fetch_sandbox(f):
         """Runs a command in a forked process with limited memory resources
         to prevent memory bomb caused by specially crafted http responses."""