rhg: add resolve_file_args to path_utils.rs...
rhg: add resolve_file_args to path_utils.rs
Extracted logic for resolving `FILE ...` arguments from cat.rs into a new
function in path_utils.rs. I plan to use this for rhg annotate.
I tried to reuse hg::utils::files::canonical_path instead, but that didn't work.
For example it reports a InsideDotHg error for any path containing "..".
