Git doesn't always write conflict markers of seven characters: the
conflict-marker-size gitattribute overrides that per file, and it is set
for good reasons — for file types whose regular content tends to contain
marker-looking lines, such as documentation about merging, or test
scripts. We hard-code seven characters everywhere we look for markers,
so none of that works.
Prepare for honoring the attribute by threading the marker size through
everything that recognizes a marker, carried on the file model. Nothing
fills it in yet, so we still use git's default size of seven everywhere,
and matching is unchanged: a marker consists of exactly that many marker
characters, and all but the "=======" one are followed by a space and a
label.
For the less common conflict types DD, AU, UA, DU, and UD, we would previously
only show "* Unmerged path" in the main view, which isn't helpful. Also, for
some of these we would split the main view and show this text both in the
unstaged changes and staged changes views, which is a bit embarrassing.
Improve this by offering more explanation about what's going on, and what the
most likely way to resolve the situation is for each case.
When enabled, it adds "+n -m" after each file in the Files panel to show how
many lines were added and deleted, as with `git diff --numstat` on the command
line.
