.mailmap: fixup entries

This patch adds no new names, but fixes the mistakes I made in the previous
commits. (94b410bba8, f4f49e225, c07a6bc57, 2013-07-12, .mailmap: Map
email addresses to names).

These mistakes are double white spaces between name and surname,
different capitalization in email address, or just the email address set
as name.

Also I forgot to include James Knight to the mailmap file.

Signed-off-by: Stefan Beller <stefanbeller@googlemail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>