Stop deleting modules (Trashcan, Flyout, Toolbox) to flag that they are disabled (bad programming technique, use a boolean instead).  Fix scrolling in Playground after adding doctype.  Fix size of arrow in Maze avatar dropdown.  Stop alerting 'false' when pegman collides with a wall.  Add default 'by' block in Playground and unit tests.
Review URL: https://codereview.appspot.com/11402044

git-svn-id: http://blockly.googlecode.com/svn/trunk@1102 c400ca83-b69d-9dd7-9705-49c6b8615e23