Git: Replace %n with %1 in string

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Change-Id: I85b584d4e53e68128279d50cb6b63e259f7a35b5
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
Move internal structures and some functions into diffutils.h

Change-Id: Ia55e556fdb8de3a2aeebf768ad9db66d840766f2
Reviewed-by: Jarek Kobus <jaroslaw.kobus@digia.com>