stpl: Add "linetype" to plot command

Seems as this should be part of an old commit (e73d15e, 'Måtte legge til
"linetype" foran -1 i plot-kommandoen', 2008-09-24 00:57:05 +0200).

94fe8338-c999-11e2-8daa-001f3b596ec9
stpl: Use suuid tag "c_stpl" instead of "stpl"

3dabab1a-c9a8-11e2-a9a6-001f3b596ec9