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

Migrated issue, originally created by Anonymous

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:
    from mako import exceptions
    from sys import stderr
    print >> sys.stderr, exceptions.text_error_template().render()

in main()

Start at the mako-render script and its main() entry point, then compare the current error handling with the behavior requested in the issue and Jinja2's debug.py exception rewriting logic. Done means template errors produce usable tracebacks when rendering non-HTML output, including through the suggested stderr path.