Revert "[FIX] fields: `digits()` computation"

This reverts commit eeedd2d9f5.

This revision introduces an issue more serious than the ones
it fixes. This is no longer possible to receive an email
aimed a sale.order thread with catchall.

To reproduce the issue:
 - Create a new sale order
 - Send a message in the thread to the customer
 - Reply to the mail received in the customer mailbox
 - Traceback, AttributeError: digits

 opw-640370

openerp/fields.py

@@ -1054,8 +1054,7 @@ class Float(Field):
     @property
     def digits(self):
         if callable(self._digits):
-            with fields._get_cursor() as cr:
-                return self._digits(cr)
+            return self._digits(fields.get_cursor())
         else:
             return self._digits
 

openerp/osv/fields.py

@@ -43,7 +43,6 @@ import pytz
 import re
 import xmlrpclib
 from operator import itemgetter
-from contextlib import contextmanager
 from psycopg2 import Binary
 
 import openerp
@@ -53,22 +52,13 @@ from openerp.tools import float_repr, float_round, frozendict, html_sanitize
 import simplejson
 from openerp import SUPERUSER_ID, registry
 
-@contextmanager
-def _get_cursor():
-    # yield a valid cursor from any environment or create a new one if none found
+def get_cursor():
+    # retrieve a valid cursor from any environment
     from openerp.api import Environment
-    from openerp.http import request
-    try:
-        request.env     # force request's env to be computed
-    except RuntimeError:
-        pass    # ignore if not in a request
     for env in Environment.envs:
         if not env.cr.closed:
-            yield env.cr
-            break
-    else:
-        with registry().cursor() as cr:
-            yield cr
+            return env.cr
+    raise RuntimeError("No valid cursor found")
 
 EMPTY_DICT = frozendict()
 
@@ -406,8 +396,7 @@ class float(_column):
     @property
     def digits(self):
         if self._digits_compute:
-            with _get_cursor() as cr:
-                return self._digits_compute(cr)
+            return self._digits_compute(get_cursor())
         else:
             return self._digits
 
@@ -1327,8 +1316,7 @@ class function(_column):
     @property
     def digits(self):
         if self._digits_compute:
-            with _get_cursor() as cr:
-                return self._digits_compute(cr)
+            return self._digits_compute(get_cursor())
         else:
             return self._digits