#199: steal/port jinja2's debug.py exception rewriting logic

The mako-render render script is useful for rendering templates in a non-html environment (eg I use it to generate c++ code ...)

It currently doesn't produce usable tracebacks when there is an error in the template. It should do something like

try:print render(data)except:frommakoimport exceptions
    fromsysimport stderr
    print>> sys.stderr, exceptions.text_error_template().render()

in main()