Support reporting within symlink/junction

This changes the matcher for source files to get the file list as real paths (resolving links) such that when the matcher checks if the file is covered from the Node.js core module path, it actually matches, since it uses realpath.

The way my Windows machines are setup, to run istanbul on code, I have to change to other drives instead of just staying on C: because istanbul is not resolving through the NTFS junctions (similar to symlinks), which is really annoying.

I originally figured this out here https://github.com/gotwarlost/istanbul/issues/197#issuecomment-43960909

This fixes #206