new symbol: ring (circle with fill=none, edge=dynamic) (merge from devbr6)

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@41245 15284696-431f-4ddb-bdfa-cd5b030d7da7

lib/symbol/symbol/extra/ring

@@ -0,0 +1,5 @@
+VERSION 1.0
+BOX -1 -1 1 1
+STRING
+  ARC 0 0 1 360 0 C
+END