Support diff 2 different filenames between 2 revisions

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Rename variable name to avoid confusion

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Fixed issue #1985: TortoiseGitBlame does not follow renames when comparing line with previous version

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Show the filename of that line

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