Merge branch 'xz/send-email-batch-size'

"git send-email" learned to overcome some SMTP server limitation
that does not allow many pieces of e-mails to be sent over a single
session.

* xz/send-email-batch-size:
  send-email: --batch-size to work around some SMTP server limit

diff --cc Documentation/config.txt
Simple merge

diff --cc Documentation/git-send-email.txt
Simple merge

diff --cc contrib/completion/git-completion.bash
Simple merge

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