split arrow into two STRINGs - main line and arms

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@70795 15284696-431f-4ddb-bdfa-cd5b030d7da7

lib/symbol/symbol/basic/arrow

@@ -4,9 +4,11 @@ STRING
   LINE
     0 -1
     0 1
-    -0.3474 0.3466 
   END
+END
+STRING
   LINE
+    -0.3474 0.3466
     0 1
     0.3474 0.3466
   END