[FIX] possible incorrect request.env

On a new database, logged as administrator, installing
``website_slides`` commonly (but not systematically) leads to a 403
error when the module install redirects to the slides
index (``/slides``).

The issue here is the installation of the slides module deletes the
existing routing map, which needs to be regenerated. The regeneration is
performed at the start of URL dispatching *before authentication* but
accesses ``request.env` in order to look up the list of installed
modules, which generates and caches (due to env being a lazy_property)
an ``Environment(cr, None, context)``.

Once regeneration and auth are done the controller is executed with
``request.env`` still being set to ``Environment(cr, None, context)``
and thus the first tentative access (search) to an object blowing up
with an AccessError. The next request or an initial request not
accessing ``request.env`` will work fine as they'll reuse the routing
map generated by the initial request.

Fixed by just getting the set of installed modules from the registry.

openerp/addons/base/ir/ir_http.py

@@ -190,14 +190,7 @@ class ir_http(osv.AbstractModel):
     def routing_map(self):
         if not hasattr(self, '_routing_map'):
             _logger.info("Generating routing map")
-            Modules = request.env['ir.module.module'].sudo()
-            installed = {
-                module.name
-                for module in Modules.search([
-                    ('state', 'in', ('installed', 'to remove', 'to upgrade')),
-                    ('name', '!=', 'web')
-                ])
-            }
+            installed = request.registry._init_modules - {'web'}
             if openerp.tools.config['test_enable']:
                 installed.add(openerp.modules.module.current_test)
             mods = [''] + openerp.conf.server_wide_modules + sorted(installed)