Merge branch 'km/send-email-getopt-long-workarounds' into maint

Even though we officially haven't dropped Perl 5.8 support, the
Getopt::Long package that came with it does not support "--no-"
prefix to negate a boolean option; manually add support to help
people with older Getopt::Long package.

* km/send-email-getopt-long-workarounds:
  git-send-email.perl: support no- prefix with older GetOptions