mailmap: Add alternative addresses for myself

At least one of these is already in-tree; it seems plausible that
others might appear too.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

.mailmap

@@ -113,6 +113,9 @@ Hanna Kruppe <hanna.kruppe@gmail.com> <robin.kruppe@gmail.com>
 Heather <heather@cynede.net> <Cynede@Gentoo.org>
 Heather <heather@cynede.net> <Heather@cynede.net>
 Herman J. Radtke III <herman@hermanradtke.com> Herman J. Radtke III <hermanradtke@gmail.com>
+Ian Jackson <ijackson@chiark.greenend.org.uk> <ian.jackson@citrix.com>
+Ian Jackson <ijackson@chiark.greenend.org.uk> <ijackson+github@slimy.greenend.org.uk>
+Ian Jackson <ijackson@chiark.greenend.org.uk> <iwj@xenproject.org>
 Ilyong Cho <ilyoan@gmail.com>
 inquisitivecrystal <22333129+inquisitivecrystal@users.noreply.github.com>
 Ivan Ivaschenko <defuz.net@gmail.com>