perl: move CPAN loader wrappers to another namespace

Move the Git::Error and Git::Mail::Address wrappers to the
Git::LoadCPAN::Loader::* namespace, e.g. Git::LoadCPAN::Error. That
module will then either load Error from CPAN (if installed on the OS),
or use Git::FromCPAN::Error.

When I added the Error wrapper in 20d2a30f8f ("Makefile: replace
perl/Makefile.PL with simple make rules", 2017-12-10) I didn't think
about how confusing it would be to have these modules sitting in the
same tree as our normal modules. Let's put these all into
Git::{Load,From}CPAN::* to clearly distinguish them from the rest.

This also makes things a bit less confusing since there was already a
Git::Error namespace ever since 8b9150e3e3 ("Git.pm: Handle failed
commands' output", 2006-06-24).

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/examples/git-difftool.perl

@@ -13,7 +13,7 @@
 use 5.008;
 use strict;
 use warnings;
-use Git::Error qw(:try);
+use Git::LoadCPAN::Error qw(:try);
 use File::Basename qw(dirname);
 use File::Copy;
 use File::Find;

git-send-email.perl

@@ -26,13 +26,13 @@ use Text::ParseWords;
 use Term::ANSIColor;
 use File::Temp qw/ tempdir tempfile /;
 use File::Spec::Functions qw(catdir catfile);
-use Git::Error qw(:try);
+use Git::LoadCPAN::Error qw(:try);
 use Cwd qw(abs_path cwd);
 use Git;
 use Git::I18N;
-use Git::Mail::Address;
 use Net::Domain ();
 use Net::SMTP ();
+use Git::LoadCPAN::Mail::Address;
 
 Getopt::Long::Configure qw/ pass_through /;
 

perl/Git.pm

@@ -104,7 +104,7 @@ increase notwithstanding).
 
 
 use Carp qw(carp croak); # but croak is bad - throw instead
-use Git::Error qw(:try);
+use Git::LoadCPAN::Error qw(:try);
 use Cwd qw(abs_path cwd);
 use IPC::Open2 qw(open2);
 use Fcntl qw(SEEK_SET SEEK_CUR);

perl/Git/LoadCPAN/Error.pm

@@ -1,11 +1,11 @@
-package Git::Error;
+package Git::LoadCPAN::Error;
 use 5.008;
 use strict;
 use warnings;
 
 =head1 NAME
 
-Git::Error - Wrapper for the L<Error> module, in case it's not installed
+Git::LoadCPAN::Error - Wrapper for the L<Error> module, in case it's not installed
 
 =head1 DESCRIPTION
 
@@ -26,13 +26,13 @@ sub import {
     } or do {
 	my $error = $@ || "Zombie Error";
 
-	my $Git_Error_pm_path = $INC{"Git/Error.pm"} || die "BUG: Should have our own path from %INC!";
+	my $Git_Error_pm_path = $INC{"Git/LoadCPAN/Error.pm"} || die "BUG: Should have our own path from %INC!";
 
 	require File::Basename;
 	my $Git_Error_pm_root = File::Basename::dirname($Git_Error_pm_path) || die "BUG: Can't figure out lib/Git dirname from '$Git_Error_pm_path'!";
 
 	require File::Spec;
-	my $Git_pm_FromCPAN_root = File::Spec->catdir($Git_Error_pm_root, 'FromCPAN');
+	my $Git_pm_FromCPAN_root = File::Spec->catdir($Git_Error_pm_root, '..', 'FromCPAN');
 	die "BUG: '$Git_pm_FromCPAN_root' should be a directory!" unless -d $Git_pm_FromCPAN_root;
 
 	local @INC = ($Git_pm_FromCPAN_root, @INC);

perl/Git/LoadCPAN/Mail/Address.pm

@@ -1,11 +1,11 @@
-package Git::Mail::Address;
+package Git::LoadCPAN::Mail::Address;
 use 5.008;
 use strict;
 use warnings;
 
 =head1 NAME
 
-Git::Mail::Address - Wrapper for the L<Mail::Address> module, in case it's not installed
+Git::LoadCPAN::Mail::Address - Wrapper for the L<Mail::Address> module, in case it's not installed
 
 =head1 DESCRIPTION