Start 1.7.5.1 maintenance track

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/RelNotes/1.7.5.1.txt

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+Git v1.7.5.1 Release Notes
+==========================
+
+Fixes since v1.7.5
+------------------
+
+ * The "--date=relative" output format used to say "X years, 12 months"
+   when it should have said "X+1 years".
+
+ * An error message from "git send-email" to diagnose a broken SMTP
+   connection configuration lacked a space between "hello=<smtp-domain>"
+   and "port=<smtp-server-port>".
+
+And other minor fixes and documentation updates.

RelNotes

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-Documentation/RelNotes/1.7.5.txt
+Documentation/RelNotes/1.7.5.1.txt