new: build the target-distribution menu from supported_dists

src/distro_info.rs

@@ -214,9 +214,12 @@ fn parse_series_csv(content: &str) -> Result<Vec<SeriesInformation>, Box<dyn Err
     Ok(series_info_list)
 }
 
-/// List the distributions known to pkh (e.g. "debian", "ubuntu")
+/// List the distributions known to pkh (e.g. "debian", "ubuntu"), sorted so
+/// that menus and error messages derived from it are deterministic
 pub fn supported_dists() -> Vec<String> {
-    DATA.dist.keys().cloned().collect()
+    let mut dists: Vec<String> = DATA.dist.keys().cloned().collect();
+    dists.sort();
+    dists
 }
 
 /// Special changelog distribution marking an entry that has not been