Approval checkmark: show full UTC datetime

This replaces the relative/fuzzy timestamp ("8 hours ago", etc.) when
hovering over an approval checkmark with the full UTC timestamp, which
is generally more useful info and can be more easily compared with
things like the time the post was made.

r2/r2/models/builder.py

@@ -48,10 +48,10 @@ from r2.lib.wrapped import Wrapped
 from r2.lib.db import operators, tdb_cassandra
 from r2.lib.filters import _force_unicode
 from r2.lib.utils import (
+    long_datetime,
     shuffle_slice,
     SimpleSillyStub,
     Storage,
-    timesince,
     to36,
     tup,
 )
@@ -299,9 +299,9 @@ class Builder(object):
                     approver = approver or _("a moderator")
 
                     if approval_time:
-                        text = _("approved by %(who)s %(when)s ago") % {
+                        text = _("approved by %(who)s at %(when)s") % {
                                     "who": approver,
-                                    "when": timesince(approval_time)}
+                                    "when": long_datetime(approval_time)}
                     else:
                         text = _("approved by %s") % approver
                     w.approval_checkmark = text