test: Add a check for too long or badly reflowed docstrings

This ensures that docstring comments are wrapped to 80 chars. ffrank
seemed to be making this mistake far too often, and it's a silly thing
to look for manually. As it turns out, I've made it too, as have many
others. Now we have a test that checks for most cases. There are still a
few stray cases that aren't checked automatically, but this can be
improved upon if someone is motivated to do so.

Before anyone complains about the 80 character limit: this only checks
docstring comments, not source code length or inline source code
comments. There's no excuse for having docstrings that are badly
reflowed or over 80 chars, particularly if you have an automated test.

pgraph/graphsync.go

@@ -38,10 +38,10 @@ func strEdgeCmpFn(e1, e2 Edge) (bool, error) {
 }
 
 // GraphSync updates the Graph so that it matches the newGraph. It leaves
-// identical elements alone so that they don't need to be refreshed.
-// It tries to mutate existing elements into new ones, if they support this.
-// This updates the Graph on success only. If it fails, then the graph won't
-// have been modified.
+// identical elements alone so that they don't need to be refreshed. It tries to
+// mutate existing elements into new ones, if they support this. This updates
+// the Graph on success only. If it fails, then the graph won't have been
+// modified.
 // FIXME: should we do this with copies of the vertex resources?
 func (obj *Graph) GraphSync(newGraph *Graph, vertexCmpFn func(Vertex, Vertex) (bool, error), vertexAddFn func(Vertex) error, vertexRemoveFn func(Vertex) error, edgeCmpFn func(Edge, Edge) (bool, error)) error {
 	oldGraph := obj.Copy() // work on a copy of the old graph