Convert constants for square type and direction to enums, and
convert if-else-if statements to switch statements.
Review URL: https://codereview.appspot.com/7431055

git-svn-id: http://blockly.googlecode.com/svn/trunk@679 c400ca83-b69d-9dd7-9705-49c6b8615e23
Adds alert if user tries to run a program with multiple top blocks on
level 1 or 2.
Review URL: https://codereview.appspot.com/7546045

git-svn-id: http://blockly.googlecode.com/svn/trunk@681 c400ca83-b69d-9dd7-9705-49c6b8615e23