Fix duplicate entries in AUTHORS

The generated AUTHORS file contains many duplicates.  If an author
has N commits, there will be N entries for the author in AUTHORS.
Check if an author already exists in the list before appending.
While at it, add a .mailmap (derived from libivrt's .mailmap) to
futher tidy the generated AUTHORS list.

.mailmap

@@ -0,0 +1,16 @@
+# 'git shortlog --help' and look for mailmap for the format of each line
+
+# Email consolidation:
+# <Preferred address in AUTHORS> <other alias used by same author>
+
+<jdenemar@redhat.com> <Jiri.Denemark@gmail.com>
+<jfehlig@suse.com> <jfehlig@novell.com>
+<stefanb@us.ibm.com> <stefanb@linux.vnet.ibm.com>
+
+# Name consolidation:
+# Preferred author spelling <preferred email>
+Alex Jia <ajia@redhat.com>
+Ján Tomko <jtomko@redhat.com>
+MATSUDA Daiki <matsudadik@intellilink.co.jp>
+Serge E. Hallyn <serge.hallyn@canonical.com>
+Philipp Hahn <hahn@univention.de>

setup.py

@@ -176,7 +176,9 @@ class my_sdist(sdist):
         f = os.popen("git log --pretty=format:'%aN <%aE>'")
         authors = []
         for line in f:
-            authors.append("   " + line.strip())
+            line = "   " + line.strip()
+            if line not in authors:
+                authors.append(line)
 
         authors.sort(key=str.lower)