OPerand now does its own expression parsing.

tests/testwhile.jet

@@ -1,7 +1,7 @@
 #!../jet-2.0
 <jet cgi="false" name1="localname" filterblanklines="true" trimlines="true">
  <set name="ix" value="1" />
- <while expr="$[ix]<10">
+ <while expr="$[ix]<=11">
   -->$[ix]<--
   <set name="ix" expr="$[ix]+1" />
  </while>