[development] security: people can no longer "administer" blocks.

[Karoly Negyesi]

What if we would add a permission or misuse an existing (administer  
filters) and simply do not show for 'lesser admins' the radio and the  
textarea under question? block configure is under new submit model so we  
can simply put in 'value' type fields and be done.

Amount of code to be written: one if, and two new form elements. 11 simple  
lines if I counted right.