Fixed FileRevs to handle renaming in another branch

Problem
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Commit B and commit C share the same parent A, but B and C are in different branches. B renamed file1 to file1.renamed, while C modified file1. C are made at a later time than B. When the branch of C is finally merged into the branch of B, commit C will appear after commit B in git log. When deciding the path of file1 at commit C, FileRevs found that the latest record in file_links table is the one related to commit B, so it used the file1.renamed as the path, which is wrong.

Solution
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Use [is_ancestor](https://github.com/MetricsGrimoire/RepositoryHandler/pull/11) method in repositoryhandler to decide whether a commit is an ancestor for another. In this case, B is not an ancestor of C. Only use the latest file_links record related to ancestors of a commit to decide the file path.

An alternative implementation is to use [commit graph](https://github.com/MetricsGrimoire/CVSAnalY/pull/40) to determine the ancestry reation. Not sure which one is better. Since #40 is not yet accepted, I try not to make this PR dependent on it.

@andygrunwald @sduenas please review, thanks!