Normalization of arrays containing self references

[naderman]

This is an issue in particular when $GLOBALS gets stuck into $context. This is something Symfony's ErrorHandler does when an error is thrown in global scope. The result is infinite recusion resulting in stack overflow on normalize().

Currently only adds a failing test.

Options are

• Limit nesting, by introducing depth counting to normalize()
• Reference detection (more complicated and uses more memory)

[naderman]

Limited depth to a hardcoded value of 9, as an implementation of option 1.

[Seldaek]

Thanks