#101 Graph marker doc. doesn't match behavior

[Neil McKay]

If .g is a graph widget, the ".g marker type foo" command
returns the class of the marker "foo", e.g. "LineMarker" or
"TextMarker". The man pages say it should return "line"
or "text". (Personally, I'd like to see the code changed
to match the documentation rather than the other way
around, so that the return value from the "marker type"
subcommand can be used in a subsequent "marker create"
command. But as long as the two are consistent I'll be
happy.)