Merge branch 'es/send-email-sendmail-alias'

"git send-email" learned to handle more forms of sendmail style aliases file. * es/send-email-sendmail-alias: send-email: further warn about unsupported sendmail aliases features t9001: add sendmail aliases line continuation tests t9001: refactor sendmail aliases test infrastructure send-email: implement sendmail aliases line continuation support send-email: simplify sendmail aliases comment and blank line recognizer send-email: refactor sendmail aliases parser send-email: fix style: cuddle 'elsif' and 'else' with closing brace send-email: drop noise comments which merely repeat what code says send-email: visually distinguish sendmail aliases parser warnings send-email: further document missing sendmail aliases functionality