HTTPS: fix python2.3, persistent connections, don't explode if SSL is not available

The urllib2 differences between python 2.3 and 2.4 are hidden by
using keepalive.py, which also gives us support for persistent
connections.

Support for HTTPS is enabled only if there's a HTTPSHandler class in
urllib2.

It's not possible to have separate classes as handlers for HTTP and
HTTPS:  to support persistent HTTPS connections, we need a class that
inherits from both keepalive.HTTPHandler and urllib2.HTTPSHandler.  If
we try to pass (an instance of) this class and (an instance of) the
httphandler class to urllib2.build_opener, this function ends up getting
confused, since both classes are subclasses of the HTTPHandler default
handler, and raises an exception.

mercurial/httprepo.py

@@ -87,11 +87,14 b' class httpconnection(keepalive.HTTPConne'
             for chunk in util.filechunkiter(data):
                 keepalive.HTTPConnection.send(self, chunk)
 
-class httphandler(keepalive.HTTPHandler):
+class basehttphandler(keepalive.HTTPHandler):
     def http_open(self, req):
         return self.do_open(httpconnection, req)
 
+has_https = hasattr(urllib2, 'HTTPSHandler')
+if has_https:
 class httpsconnection(httplib.HTTPSConnection):
+        response_class = keepalive.HTTPResponse
     # must be able to send big bundle as stream.
 
     def send(self, data):
@@ -103,9 +106,12 b' class httpsconnection(httplib.HTTPSConne'
             for chunk in util.filechunkiter(data):
                 httplib.HTTPSConnection.send(self, chunk)
 
-class httpshandler(urllib2.HTTPSHandler):
+    class httphandler(basehttphandler, urllib2.HTTPSHandler):
     def https_open(self, req):
         return self.do_open(httpsconnection, req)
+else:
+    class httphandler(basehttphandler):
+        pass
 
 class httprepository(remoterepository):
     def __init__(self, ui, path):
@@ -176,7 +182,6 b' class httprepository(remoterepository):'
 
         opener = urllib2.build_opener(
             handler,
-            httpshandler(),
             urllib2.HTTPBasicAuthHandler(passmgr),
             urllib2.HTTPDigestAuthHandler(passmgr))
 
@@ -322,4 +327,8 b' class httprepository(remoterepository):'
             os.unlink(tempname)
 
 class httpsrepository(httprepository):
-    pass
+    def __init__(self, ui, path):
+        if not has_https:
+            raise util.Abort(_('Python support for SSL and HTTPS '
+                               'is not installed'))
+        httprepository.__init__(self, ui, path)