[m-rev.] diff: add date_time/0 as a synonym for date/0

[Julien Fischer]

This change has already been discussed back here: 
<http://www.mercurylang.org/list-archives/developers/2013-February/015799.html>.

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Add date_time/0 as a synonym for date/0.

library/calendar.m:
 	As above.

Julien.

diff --git a/library/calendar.m b/library/calendar.m
index f5ed62c..55c1825 100644
--- a/library/calendar.m
+++ b/library/calendar.m
@@ -34,6 +34,10 @@
      %
  :- type date.

+    % A more meaningful name for the above.
+    %
+:- type date_time == date.
+
      % Date components.
      %
  :- type year == int.         % Year 0 is 1 BC, -1 is 2 BC, etc.