[stringtemplate-interest] bug in format option

[Terence Parr]

Wow!  Nasty bug.  As usual, John, excellent analysis and solution.  I  
think just killing the formatString is ok:

	protected void handleExprOptions(StringTemplate self) {
		// make sure options don't use format / renderer.  They are usually
		// strings which might invoke a string renderer etc...
		formatString = null;
...

Try that.  I pushed to depot.

Ter