[FIX] setup Environment for the report thread

When launching an old-style webkit report, the service launches the rendering in a new thread - which has a fresh set of local variables -, but fails to setup the Environment, so it crashes when it tries to create a new instance in the browse method of the BaseModel.

The patch submitted solves the problem by wrapping the code in the new thread with Environment.manage().

The stack trace is:
```python
  File "odoo/openerp/service/report.py", line 92, in go
    result, format = openerp.report.render_report(cr, uid, ids, object, datas, context)
  File "odoo/openerp/report/__init__.py", line 40, in render_report
    return registry['ir.actions.report.xml'].render_report(cr, uid, ids, name, data,
context)
  File "odoo/openerp/api.py", line 204, in wrapper
    return old_api(self, *args, **kwargs)
  File "odoo/openerp/addons/base/ir/ir_actions.py", line 150, in render_report
    return new_report.create(cr, uid, res_ids, data, context)
  File "odoo/openerp/report/report_sxw.py", line 352, in create
    registry['res.font'].font_scan(cr, SUPERUSER_ID, lazy=True, context=context)
  File "odoo/openerp/api.py", line 204, in wrapper
    return old_api(self, *args, **kwargs)
  File "odoo/openerp/addons/base/res/res_font.py", line 85, in font_scan
    self._scan_disk(cr, uid, context=context)
  File "odoo/openerp/api.py", line 204, in wrapper
    return old_api(self, *args, **kwargs)
  File "odoo/openerp/addons/base/res/res_font.py", line 118, in _scan_disk
    }, context=context)
  File "odoo/openerp/api.py", line 204, in wrapper
    return old_api(self, *args, **kwargs)
  File "odoo/openerp/api.py", line 296, in old_api
    recs = self.browse(cr, uid, [], context)
  File "odoo/openerp/api.py", line 204, in wrapper
    return old_api(self, *args, **kwargs)
  File "odoo/openerp/models.py", line 5025, in browse
    return self._browse(Environment(cr, uid, context or {}), ids)
  File "odoo/openerp/api.py", line 666, in __new__
    env, envs = None, cls._local.environments
  File "/usr/lib/python2.7/dist-packages/werkzeug/local.py", line 70, in __getattr__
    raise AttributeError(name)
AttributeError: environments
```