Return for an empty bufname in s:gotoline
Use `:argdo` instead of `:bufdo` in `s:startup`

Drop calls to `doautocmd FileType` and `doautocmd BufEnter` - only
`Syntax` needs to be called manually.
Not sure about the call to `:diffthis` for `&diff` - is `vimdiff foo:5
bar:6` supposed to work?