Allow jet script to not begin with jet tag. Treat as container.

tests/testrandom.jet

@@ -1,7 +1,10 @@
 #!../jet-2.0
+This is a test
+<set name="var1" value="abc" />
 <jet cgi="true" name1="localname" filterblanklines="true" trimlines="true">
  <for name="ix" start="1" end="20" step="1">
   <set name="random" expr="random()" />
   $[random]
  </for>
 </jet>
+$[var1]