Simpler movements of guides, needs cleanup, saving it for now.
If a guide line is horiz or vert then allow the user to grab and drag
it without converting it to a curve.

This commit also introduces SPLFirstVisit() for visiting the points of
an spl without needing the iteration mechanics each time.
Merge pull request #665 from monkeyiq/2013aug/guides

 If a guide line is horiz or vert then allow the user to grab and drag  it without converting it to a curve.