cvsimport: work around perl tzset issue

On many platforms, the first invocation of localtime_r will
check $TZ in the environment, but subsequent invocations
will use a cached value. That means that setting $ENV{TZ} in
the middle of the program may or may not have an effect on
later calls to localtime.  Perl 5.10.0 and later handles
this automatically for us, but we try to remain portable
back to 5.8. Work around it by calling tzset ourselves.

git-cvsimport.perl

@@ -24,11 +24,11 @@
 use Time::Local;
 use IO::Socket;
 use IO::Pipe;
-use POSIX qw(strftime dup2 ENOENT);
+use POSIX qw(strftime tzset dup2 ENOENT);
 use IPC::Open2;
 
 $SIG{'PIPE'}="IGNORE";
-$ENV{'TZ'}="UTC";
+set_timezone('UTC');
 
 our ($opt_h,$opt_o,$opt_v,$opt_k,$opt_u,$opt_d,$opt_p,$opt_C,$opt_z,$opt_i,$opt_P, $opt_s,$opt_m,@opt_M,$opt_A,$opt_S,$opt_L, $opt_a, $opt_r, $opt_R);
 my (%conv_author_name, %conv_author_email, %conv_author_tz);
@@ -99,6 +99,15 @@ ($)
 	close ($f);
 }
 
+# Versions of perl before 5.10.0 may not automatically check $TZ each
+# time localtime is run (most platforms will do so only the first time).
+# We can work around this by using tzset() to update the internal
+# variable whenever we change the environment.
+sub set_timezone {
+	$ENV{TZ} = shift;
+	tzset();
+}
+
 # convert getopts specs for use by git config
 my %longmap = (
 	'A:' => 'authors-file',
@@ -854,9 +863,9 @@ sub commit {
 		}
 	}
 
-	$ENV{'TZ'}=$author_tz;
+	set_timezone($author_tz);
 	my $commit_date = strftime("%s %z", localtime($date));
-	$ENV{'TZ'}="UTC";
+	set_timezone('UTC');
 	$ENV{GIT_AUTHOR_NAME} = $author_name;
 	$ENV{GIT_AUTHOR_EMAIL} = $author_email;
 	$ENV{GIT_AUTHOR_DATE} = $commit_date;