Run mono with the --debug option

This tells mono to load the debug information and lets the unit testing
framework show stack traces with line numbers in them, which is quite
handy.
Update libgit2 to f29e489

https://github.com/libgit2/libgit2/compare/65e9dc6...f29e489
Bind git_remote_fetch()
Bind git_reference_remove()
Enable now passing test assertion