tzset.3: Clarify "daylight" and remove erroneous note.

When tzset is run the value of daylight is computed by looking at all available rules for the application of daylight savings. This includes reading the tzdata files to determine if there is a transition or not for the current timezone. It also includes parsing TZ env to see if it specifies custom rules which are used in precedence to any tzdata rules. Therefore daylight is going to be set if there is a daylight saving rule past, present, or future that indicates a transition. We clarify that in the man page.

Lastly, the note about tz_dsttime is not correct and is removed. The earlier paragraph about daylight makes it clear that it doesn't mean "daylight saving rule applies now", and the interaction with tz_dsttime is not correct for glibc on Linux (as outlined in my gettimeofday.3 patch sent here: http://marc.info/?l=linux-man&m=144977768703615&w=2).

Signed-off-by Carlos O'Donell <[email protected]>

---
Cheers,
Carlos.

man3/tzset.3 +2 -8

index 545bd9c..4786dd9 100644
@@ -70,8 +70,8 @@ This function is automatically called by the
 other time conversion functions that depend on the timezone.
 In a System-V-like environment, it will also set the variables \fItimezone\fP
 (seconds West of UTC) and \fIdaylight\fP (to 0 if this timezone does not
-have any daylight saving time rules, or to nonzero if there is a time during
-the year when daylight saving time applies).
+have any daylight saving time rules, or to nonzero if there is a time,
+past, present or future when daylight saving time applies).
 .PP
 If the
 .B TZ

@@ -223,12 +223,6 @@ T}	Thread safety	MT-Safe env locale
 .SH CONFORMING TO
 POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
 .SH NOTES
-Note that the variable \fIdaylight\fP does not indicate that daylight
-saving time applies right now.
-It used to give the number of some
-algorithm (see the variable \fItz_dsttime\fP in
-.BR gettimeofday (2)).
-It has been obsolete for many years but is required by SUSv2.
 .LP
 4.3BSD had a function
 .BI "char *timezone(" zone ", " dst )