Finished up the keyword resolution issue and fixed for, while and until. Other tags still need work.

tests/testwhile.jet

@@ -2,8 +2,7 @@
 <jet cgi="false" name1="localname" filterblanklines="true" trimlines="true">
  <set name="ix" value="1" />
  <while expr="$[ix]<10">
-  <set name="check" expr="$[ix]<10" />
-  -->$[check]-$[ix]<--
+  -->$[ix]<--
   <set name="ix" expr="$[ix]+1" />
  </while>
 </jet>