bug#21902: doc incorrectly describes Julian Date

[Zefram <zefram@fysh.org>]

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Andy Wingo wrote:
>Would you like to propose a specific patch to the documentation?

Sure.  Patch attached.

-zefram

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--- a/doc/ref/srfi-modules.texi	2014-03-20 20:21:21.000000000 +0000
+++ b/doc/ref/srfi-modules.texi	2016-06-24 18:57:59.088243245 +0100
@@ -2461,8 +2461,8 @@
 @cindex UTC
 @cindex TAI
 This module implements time and date representations and calculations,
-in various time systems, including universal time (UTC) and atomic
-time (TAI).
+in various time systems, including Coordinated Universal Time (UTC)
+and International Atomic Time (TAI).
 
 For those not familiar with these time systems, TAI is based on a
 fixed length second derived from oscillations of certain atoms.  UTC
@@ -2494,18 +2494,12 @@
 @cindex julian day
 @cindex modified julian day
 Also, for those not familiar with the terminology, a @dfn{Julian Day}
-is a real number which is a count of days and fraction of a day, in
-UTC, starting from -4713-01-01T12:00:00Z, ie.@: midday Monday 1 Jan
-4713 B.C.  A @dfn{Modified Julian Day} is the same, but starting from
-1858-11-17T00:00:00Z, ie.@: midnight 17 November 1858 UTC.  That time
-is julian day 2400000.5.
-
-@c  The SRFI-1 spec says -4714-11-24T12:00:00Z (November 24, -4714 at
-@c  noon, UTC), but this is incorrect.  It looks like it might have
-@c  arisen from the code incorrectly treating years a multiple of 100
-@c  but not 400 prior to 1582 as non-leap years, where instead the Julian
-@c  calendar should be used so all multiples of 4 before 1582 are leap
-@c  years.
+is a real number which is a count of days and fraction of a day, in UT,
+starting from -4713-11-24T12:00:00Z, ie.@: midday UT on Monday 24 November
+4714 BC in the proleptic Gregorian calendar (1 January 4713 BC in the
+proleptic Julian calendar).  A @dfn{Modified Julian Day} is the same,
+but starting from 1858-11-17T00:00:00Z, ie.@: midnight UT on Wednesday
+17 November AD 1858.  That time is julian day 2400000.5.
 
 
 @node SRFI-19 Time