vimdiff unit tests

$ bash mergetools/vimdiff
Test Case #00: OK
Test Case #01: OK
Test Case #02: OK
Test Case #03: OK
Test Case #04: OK
Test Case #05: OK
Test Case #06: OK
Test Case #07: OK
Test Case #08: OK
Test Case #09: OK
Test Case #10: OK
Test Case #11: OK
Test Case #12: OK
Test Case #13: OK