handle all types of aliases for the contributor list

If a contributor email is already in the list we won't create a new
entry. However, if the name is different than in the list, we print a
message if an alias is missing in .mailmap

If an email is not in the list, but the name is in the list this could
mean two things:

 1. Two different persons have the same name.
    This is possible, but less likely than 2.
 2. A contributor used another mail.
    This is likely the case and we don't make a new entry,
    but print a message.

.mailmap

@@ -1,2 +1,5 @@
 Andrew Brown <brownan@gmail.com> <andrew@fry.(none)>
 Alex Headley <aheadley@waysaboutstuff.com> <aheadley@nexcess.net>
+Alex Headley <aheadley@waysaboutstuff.com> aheadley
+Michael Fallows <michael@fallo.ws> redorkulated
+Maciej Malecki <maciej.malecki@hotmail.com> Maciej Małecki