added apology/explanation comment to arrow sections of makeEdge()

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/gridgraph@50 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
improved commenting on hacks in methods.R

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/gridgraph@51 edb9625f-4e0d-4859-8d74-9fd3b1da38cb