Another thin arrow GIMP Python plug-in called 'ArrowsCreator'.
It's characteristics are:
-produces many different types of straight arrows
-produces one type of 'path' arrow
-facilitates combination of multiple arrows
-interactive with GIMP
-developed on GIMP 2.6 (work on 2.8 except no repeat gradient in shaft and GIMP don't control brush size).
ATTENTION: don't change layer during execution of the plug-in. Also on my computer begin to get sluggish for certain type of arrow in image greater than 7 Mpx.