Add "safety compilation". Improved, fixed messages

- node ext searcher also looks for "iojs" if no node(js?) found.
- koch ensures the local work dir compiler is freshly compiled before executing the tests.
- the tester can only run in the repo dir - now the compiler and libs used are also explicitly the local dirs - so no confusion from system wide pathing ("sufficiently sandboxed").
- fixed expectations in tmitems.nim test to match changes in json mod.
- re-layouted the columns / row printing slightly, making test fails pop out more, and everything "normal" layed back.

compiler/nodejs.nim

@@ -4,3 +4,5 @@ proc findNodeJs*(): string =
   result = findExe("nodejs")
   if result == "":
     result = findExe("node")
+  if result == "":
+    result = findExe("iojs")