Enable comments and warnings to be opened/closed on non-editable blocks.

Review URL: https://codereview.appspot.com/48900043

git-svn-id: http://blockly.googlecode.com/svn/trunk@1595 c400ca83-b69d-9dd7-9705-49c6b8615e23
Fix XML-generated disabled blocks.  Issue 173.

R=spertus@google.com

Review URL: https://codereview.appspot.com/48970043

git-svn-id: http://blockly.googlecode.com/svn/trunk@1597 c400ca83-b69d-9dd7-9705-49c6b8615e23