Make includes similar to original libsvn_diff

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Sync libsvn_diff from subversion r876937

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Fixed issue #1728: TortoiseGitMerge show fake difference in the same lines if line end falls to 0x40000 byte

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>