- create and use a ContactIds type as an ordered set instead of "Vec<u32>".

- recreate the group list more carefully, fixes #985

- resultify a few functions in the dc_receive pipeline

- don't quote displaynames in email-addresses, use utf8, preliminrarily addresses #976

examples/repl/cmdline.rs

@@ -94,7 +94,9 @@ pub fn dc_reset_tables(context: &Context, bits: i32) -> i32 {
 fn dc_poke_eml_file(context: &Context, filename: impl AsRef<Path>) -> Result<(), Error> {
     let data = dc_read_file(context, filename)?;
 
-    dc_receive_imf(context, &data, "import", 0, 0);
+    if let Err(err) = dc_receive_imf(context, &data, "import", 0, 0) {
+        println!("dc_receive_imf errored: {:?}", err);
+    }
     Ok(())
 }