rhg: Sort config files when adding a directory

For example in `/etc/mercurial/hgrc.d/` or with `HGRCPATH=some-directory`.
Previously files where parsed in the order returned by the filesystem,
which is undefined. But order is significant when multiple files
define the same configuration key: the "last" one wins.

Differential Revision: https://phab.mercurial-scm.org/D10111

rust/hg-core/src/config/config.rs

@@ -125,8 +125,13 b' impl Config {'
             .when_reading_file(path)
             .io_not_found_as_none()?
         {
-            for entry in entries {
-                let file_path = entry.when_reading_file(path)?.path();
+            let mut file_paths = entries
+                .map(|result| {
+                    result.when_reading_file(path).map(|entry| entry.path())
+                })
+                .collect::<Result<Vec<_>, _>>()?;
+            file_paths.sort();
+            for file_path in &file_paths {
                 if file_path.extension() == Some(std::ffi::OsStr::new("rc")) {
                     self.add_trusted_file(&file_path)?
                 }