Be a little smarter about invisible characters in terminal prompts This is a partial fix to #8724. Previously, only known color codes were considered to be invisible. Now, it looks for any kind of invisible sequence as defined by the \001 \002 delimiters (which is what readline uses). The situation could still be improved, as it still assumes that the number of invisible characters is constant for a given template. Making this work correctly with the existing API is awkward, so I didn't attempt it, especially since the readline frontend may be removed at some point in the near future.