Teammates: Fix infinite redirects when serving unknown URLs

[whipermr5]

Environment

Live server at V5.98

Steps to reproduce

Visit http://teammatesv4.appspot.com/abc

Expected behaviour

Fail gracefully with a 404 status code and error page

Actual behaviour

[Dartteon]

Is this bug able to be replicated on localhost? Somehow, I just get redirected to Error 404 page upon invalid URLs. (I'm on latest master)

[whipermr5]

Need staging server to replicate; it seems like an issue with GAE's default handler servlet.

[HirdayGupta]

Found some threads facing a similar issue:

• A (temporary?) workaround is suggested in an answer at StackOverflow here(http://stackoverflow.com/questions/12293934/google-app-engine-endless-redirect-with-a-filter-mapped-to).
• A possible (but vaguely worded) solution is on the comment by "gk" here.

@whipermr5 take a look at them and see if you find any of them viable. Will get started working on it once you revert.

[whipermr5]

@HirdayGupta The first one looks viable :)