SF 658405: calendar.py to rely on the datetime module instead of the time
module.
The code is shorter, more readable, faster, and dramatically increases the
range of acceptable dates.
Also, used the floor division operator in leapdays().
diff --git a/Doc/lib/libcalendar.tex b/Doc/lib/libcalendar.tex
index 222e2db..bf0c85b 100644
--- a/Doc/lib/libcalendar.tex
+++ b/Doc/lib/libcalendar.tex
@@ -15,10 +15,12 @@
week to Sunday (6) or to any other weekday. Parameters that specify
dates are given as integers.
-Most of these functions rely on the platform provided \function{mktime()}.
-Therefore, valid argument values may vary from system to system.
-On Unix, valid years are typically between \code{1970} and \code{2037},
-but may be work between \code{1902} and \code{2037}.
+Most of these functions rely on the \module{datetime} module which
+uses an idealized calendar, the current Gregorian calendar indefinitely
+extended in both directions. This matches the definition of the
+"proleptic Gregorian" calendar in Dershowitz and Reingold's book
+"Calendrical Calculations", where it's the base calendar for all
+computations.
\begin{funcdesc}{setfirstweekday}{weekday}
Sets the weekday (\code{0} is Monday, \code{6} is Sunday) to start