ResolveMerger: Fix the issue with binary modify-modify conflicts

ResolveMerger: Fix the issue with binary modify-modify conflicts

1) If the file was marked as binary by git attributes, we should add the
path to conflicts if content differs in OURS and THEIRS
2) If the path is a file in OURS, THEIRS and BASE and if it is a binary
in any one of them, no content merge should be attempted and the file
content is kept as is in the work tree

Bug: jgit-14
Change-Id: I9201bdc53a55f8f40adade4b6a36ee8ae25f4db8