[stringtemplate-interest] fixed if-condition thing

[Terence Parr]

o IF with false condition results in missing not empty value. So,
   <names:{n | <if(n.cool)><n><endif>}; separator=",">
   doesn't emit a separator for non-cool names. See
   http://www.antlr.org/pipermail/stringtemplate-interest/2009-July/002020.html

   WARNING: You now pay a penalty now for a separator.  It writes each  
element to
   a temp buffer before emitting.  Expensive.
   Later, I can optimize to check if one chunk in template and it's a  
conditional.

it's only in the depot.

Ter