Improve error reporting when a loop is detected

[sbulen]

Description

In our error functions, we have some pretty good loop detection, and even produce a backtrace when a loop is detected.

BUT...

We do not capture the actual error that caused the loop. We just display the backtrace:

SMF/Sources/Errors.php

Line 51 in 4d7fbd8

die('Error loop.');

We need to display the actual db error message as well.

Knowing we are in a loop isn't anywhere near as helpful as knowing WHY we're in a loop...

We have seen a couple of these lately...

Additional information/references

Without the error, you're flying blind, as in these forum support requests:
https://www.simplemachines.org/community/index.php?topic=586471.0
https://www.simplemachines.org/community/index.php?topic=586373.0