Simplify the root status logic

Simplify the root status logic

Go through fileStatus like other cases to make sure that all use
cases go through the same code path. This also makes sure to use
lookupProblem which will use lower_bound which is more efficient
for larger sets of sync problems.

This also fixes the issue with lookupProblem that prevented it to
properly match an empty pathToMatch, caused by the fact that the
problem map contains relative paths not starting with a slash.