PatchCoverage now checks new file name, and new start number for chunks

This tweaks the patch coverage class, so that it reads the new file name, rather than the old file name in case of a moved file in git.

This also fixes an issue where the wrong line numbers are being output. If there are multiple chunks in a given patch that add/remove lines, the later chunks patch coverage line numbers become mis-aligned
Apologies, didn't look like there were any other contributors other than sb in the files I had looked at, didn't realise.