Merge branch 'ja/do-not-ask-needless-questions'

Git sometimes gives an advice in a rhetorical question that does
not require an answer, which can confuse new users and non native
speakers.  Attempt to rephrase them.

* ja/do-not-ask-needless-questions:
  git-filter-branch: be more direct in an error message
  read-tree -m: make error message for merging 0 trees less smart aleck
  usability: don't ask questions if no reply is required

builtin/am.c

@@ -1312,7 +1312,7 @@ static int parse_mail(struct am_state *state, const char *mail)
 	}
 
 	if (is_empty_file(am_path(state, "patch"))) {
-		printf_ln(_("Patch is empty. Was it split wrong?"));
+		printf_ln(_("Patch is empty."));
 		die_user_resolve(state);
 	}
 
@@ -1931,7 +1931,8 @@ static void am_resolve(struct am_state *state)
 
 	if (unmerged_cache()) {
 		printf_ln(_("You still have unmerged paths in your index.\n"
-			"Did you forget to use 'git add'?"));
+			"You should 'git add' each file with resolved conflicts to mark them as such.\n"
+			"You might run `git rm` on a file to accept \"deleted by them\" for it."));
 		die_user_resolve(state);
 	}