[PATCH 2/3] Fix get_tz_offset to properly handle DST boundary cases

[Ben Walton <bdwalton@gmail.com>]

When passed a local time that was on the boundary of a DST change,
get_tz_offset returned a GMT offset that was incorrect (off by one
hour).  This is because the time was converted to GMT and then back to
a time stamp via timelocal() which cannot disambiguate boundary cases
as noted in its documentation.

Modify this algorithm, using an approach suggested by Junio C Hamano
that obtains the GMT time stamp by using timegm(localtime()) instead
of timelocal(gmtime()).  This avoids the ambigious conversion and
allows a correct time to be returned on every occassion.

Signed-off-by: Ben Walton <bdwalton@gmail.com>
---
 perl/Git.pm |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/perl/Git.pm b/perl/Git.pm
index 5649bcc..a56d1e7 100644
--- a/perl/Git.pm
+++ b/perl/Git.pm
@@ -103,7 +103,7 @@ use Error qw(:try);
 use Cwd qw(abs_path cwd);
 use IPC::Open2 qw(open2);
 use Fcntl qw(SEEK_SET SEEK_CUR);
-use Time::Local qw(timelocal);
+use Time::Local qw(timegm);
 }
 
 
@@ -528,8 +528,8 @@ If TIME is not supplied, the current local time is used.
 sub get_tz_offset {
 	# some systmes don't handle or mishandle %z, so be creative.
 	my $t = shift || time;
-	my $gm = timelocal(gmtime($t));
-	my $sign = qw( + + - )[ $t <=> $gm ];
+	my $gm = timegm(localtime($t));
+	my $sign = qw( + + - )[ $gm <=> $t ];
 	return sprintf("%s%02d%02d", $sign, (gmtime(abs($t - $gm)))[2,1]);
 }
 
-- 
1.7.10.4