config: tell the user that we expect an ASCII character

Commit 50b54fd (config: be strict on core.commentChar, 2014-05-17)
notes that “multi-byte character encoding could also be misinterpreted”,
and indeed a multi-byte codepoint (non-ASCII) is not accepted as a valid
`core.commentChar`.

Signed-off-by: Kristoffer Haugsbakk <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: LemmingAvalanche

config.c

@@ -1686,7 +1686,7 @@ static int git_default_core_config(const char *var, const char *value, void *cb)
 			comment_line_char = value[0];
 			auto_comment_line_char = 0;
 		} else
-			return error(_("core.commentChar should only be one character"));
+			return error(_("core.commentChar should only be one ASCII character"));
 		return 0;
 	}