Provide a way to disable hostname canonicalization

[mithrandi]

The ability to have multiple canonical hostnames was planned previously, but for sites that don't need to use the websharing-by-username-in-hostname feature, there's no real need to care about canonicalization; resources can just be served from whatever hostname the page was requested from. All that is required is a way to turn off the canonicalization.

[mithrandi]

Very rough sketch of how to implement this, copied from an ad-hoc patch we have deployed already:

===================================================================
--- Mantissa/xmantissa/publicweb.py (revision 18024)
+++ Mantissa/xmantissa/publicweb.py (working copy)
@@ -805,7 +805,7 @@
         action' and 'error' slots in the template accordingly.
         """
         generator = ixmantissa.ISiteURLGenerator(self.store)
-        url = generator.rootURL(IRequest(ctx))
+        url = URL.fromString('/')
         url = url.child('__login__')
         for seg in self.segments:
             url = url.child(seg)
Index: Mantissa/xmantissa/web.py
===================================================================
--- Mantissa/xmantissa/web.py   (revision 18024)
+++ Mantissa/xmantissa/web.py   (working copy)
@@ -148,10 +148,11 @@
             this website is available.
         """
         host = request.getHeader('host') or self.hostname
-        if ':' in host:
-            host = host.split(':', 1)[0]
-        if (host == self.hostname or
-            host.startswith('www.') and host[len('www.'):] == self.hostname):
+        #if ':' in host:
+        #    host = host.split(':', 1)[0]
+        #if (host == self.hostname or
+        #    host.startswith('www.') and host[len('www.'):] == self.hostname):
+        if True:
             return URL(scheme='', netloc='', pathsegs=[''])
         else:
             if request.isSecure():
@@ -365,7 +366,7 @@
         """
         if getattr(self.wrappedResource, 'needsSecure', False):
             request = IRequest(context)
-            url = self.urlGenerator.encryptedRoot()
+            url = self.urlGenerator.encryptedRoot(request.getHeader('Host'))
             if url is not None:
                 for seg in request.prepath:
                     url = url.child(seg)

I think the change to publicweb is not actually needed given the change to SiteConfiguration but this needs to be tested.