Merge branch 'ab/require-perl-5.8' into maint

* ab/require-perl-5.8:
perl: use "use warnings" instead of -w
perl: bump the required Perl version to 5.8 from 5.6.[21]

diff --cc git-relink.perl
Simple merge

diff --cc git-send-email.perl
Simple merge

diff --cc git-svn.perl
Simple merge