perl: bump the required Perl version to 5.8 from 5.6.[21]

Formalize our dependency on perl 5.8, bumped from 5.6.[12]. We already
used the three-arg form of open() which was introduced in 5.6.1, but
t/t9700/test.pl explicitly depended on 5.6.2.

However git-add--interactive.pl has been failing on the 5.6 line since
it was introduced in v1.5.0-rc0~12^2~2 back in 2006 due to this open
syntax:

    sub run_cmd_pipe {
           my $fh = undef;
           open($fh, '-|', @_) or die;
           return <$fh>;
    }

Which when executed dies on "Can't use an undefined value as
filehandle reference". Several of our tests also fail on 5.6 (even
more when compiled with NO_PERL_MAKEMAKER=1):

    t2016-checkout-patch.sh
    t3904-stash-patch.sh
    t3701-add-interactive.sh
    t7105-reset-patch.sh
    t7501-commit.sh
    t9700-perl-git.sh

Our code is bitrotting on 5.6 with no-one interested in fixing it, and
pinning us to such an ancient release of Perl is keeping us from using
useful features introduced in the 5.8 release.

The 5.6 series is now over 10 years old, and the 5.6.2 maintenance
release almost 7. 5.8 on the other hand is more than 8 years old.

All the modern Unix-like operating systems have now upgraded to it or
a later version, and 5.8 packages are available for old IRIX, AIX
Solaris and Tru64 systems.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Acked-by: Tor Arntsen <tor@spacetec.no>
Acked-by: Randal L. Schwartz <merlyn@stonehenge.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

INSTALL

@@ -67,10 +67,10 @@ Issues of note:
 	- A POSIX-compliant shell is required to run many scripts needed
 	  for everyday use (e.g. "bisect", "pull").
 
-	- "Perl" is needed to use some of the features (e.g. preparing a
-	  partial commit using "git add -i/-p", interacting with svn
-	  repositories with "git svn").  If you can live without these, use
-	  NO_PERL.
+	- "Perl" version 5.8 or later is needed to use some of the
+	  features (e.g. preparing a partial commit using "git add -i/-p",
+	  interacting with svn repositories with "git svn").  If you can
+	  live without these, use NO_PERL.
 
 	- "openssl" library is used by git-imap-send to use IMAP over SSL.
 	  If you don't need it, use NO_OPENSSL.

git-add--interactive.perl

@@ -1,5 +1,6 @@
 #!/usr/bin/perl -w
 
+use 5.008;
 use strict;
 use Git;
 

git-archimport.perl

@@ -54,6 +54,7 @@ and can contain multiple, unrelated branches.
 
 =cut
 
+use 5.008;
 use strict;
 use warnings;
 use Getopt::Std;

git-cvsexportcommit.perl

@@ -1,5 +1,6 @@
 #!/usr/bin/perl -w
 
+use 5.008;
 use strict;
 use Getopt::Std;
 use File::Temp qw(tempdir);

git-cvsimport.perl

@@ -13,6 +13,7 @@
 # The head revision is on branch "origin" by default.
 # You can change that with the '-o' option.
 
+use 5.008;
 use strict;
 use warnings;
 use Getopt::Long;

git-cvsserver.perl

@@ -15,6 +15,7 @@
 ####
 ####
 
+use 5.008;
 use strict;
 use warnings;
 use bytes;

git-difftool.perl

@@ -10,6 +10,7 @@
 #
 # Any arguments that are unknown to this script are forwarded to 'git diff'.
 
+use 5.008;
 use strict;
 use warnings;
 use Cwd qw(abs_path);

git-relink.perl

@@ -6,7 +6,7 @@
 #
 # Scan two git object-trees, and hardlink any common objects between them.
 
-use 5.006;
+use 5.008;
 use strict;
 use warnings;
 use Getopt::Long;

git-send-email.perl

@@ -16,6 +16,7 @@
 #    and second line is the subject of the message.
 #
 
+use 5.008;
 use strict;
 use warnings;
 use Term::ReadLine;

git-svn.perl

@@ -1,6 +1,7 @@
 #!/usr/bin/env perl
 # Copyright (C) 2006, Eric Wong <normalperson@yhbt.net>
 # License: GPL v2 or later
+use 5.008;
 use warnings;
 use strict;
 use vars qw/	$AUTHOR $VERSION

gitweb/gitweb.perl

@@ -7,6 +7,7 @@
 #
 # This program is licensed under the GPLv2
 
+use 5.008;
 use strict;
 use warnings;
 use CGI qw(:standard :escapeHTML -nosticky);

perl/Git.pm

@@ -7,6 +7,7 @@ Git - Perl interface to the Git version control system
 
 package Git;
 
+use 5.008;
 use strict;
 
 

t/t7006/test-terminal.perl

@@ -1,4 +1,5 @@
 #!/usr/bin/perl
+use 5.008;
 use strict;
 use warnings;
 use IO::Pty;

t/t9700/test.pl

@@ -1,7 +1,7 @@
 #!/usr/bin/perl
 use lib (split(/:/, $ENV{GITPERLLIB}));
 
-use 5.006002;
+use 5.008;
 use warnings;
 use strict;