ENH prevent redirect loop

[IgorNadj]

To reproduce, rename your framework directory to framework2 (to simulate a missing framework) and make a http request.

Before change, the reponse is 500 Internal Server Error, and the error is (apache/error.log):
"AH00124: Request exceeded the limit of 10 internal redirects due to probable configuration error. ..."

After change, the response is 404 Not Found, and contains helpful error message:
"The requested URL /framework/main.php was not found on this server"

Note: I'm not sure exactly where this code should go, if it's the first rule or after http basic auth etc.

[tractorcow]

The correct response code is 500; The server is incorrectly configured.

A 404 implies that the user requested a url where no resource exists.

[IgorNadj]

It's true that the 404 is misleading, however an apache error is misleading as well. It's an app error really, the app's .htaccess is not doing anything useful, but instead getting stuck in a redirect loop.

I've just seen the file install-frameworkmissing.html, perhaps it should redirect there?

## Internal Redirect Loop Protection
    RewriteCond %{ENV:REDIRECT_STATUS} 200
    RewriteRule ^ install-frameworkmissing.html [L]

[dhensby]

That latest suggestion makes sense.

[IgorNadj]

This seems to false-alarm. Very dangerous to put in, for relatively minor benefits. Closing PR.