Merge branch 'nz/send-email-headers-are-case-insensitive'

When user spells "cc:" in lowercase in the fake "header" in the trailer part, send-email failed to pick up the addresses from there. As e-mail headers field names are case insensitive, this script should follow suit and treat "cc:" and "Cc:" the same way. * nz/send-email-headers-are-case-insensitive: git-send-email: treat field names as case-insensitively