Fix loading of configuration files

This contains 94 commits, but it really consists of 3 changes:

1. Merge a more recent version of NGit which contains numerous bug fixes to the Sharpen library (this gets things close to working)
2. Make a final correction to the `FilePath` constructor to work with volume separator character on Windows (in particular for the `:` in `C:`)
3. Revert commit eb6da2cc07359c96dd8d97cbf13d85c5ba0b4949 so configuration files will load