Log backtrace of PHP errors and exceptions

As the author wrote, the one being worked on core is too large and probably too slow on the uptake.

In D8 it is perfectly possible to deal with this from contrib without hacking core. That might be a better place for this to move on...

Is this a duplicate of #2638140: Error logging should log a backtrace consistently?

An updated patch to keep up with a change to _drupal_log_error()

Here is an updated patch that uses several variables to optionally provide the "heavy" or "light" version. The previous patch calls debug_backtrace as the "heavy" version and then unsets array elements to make it light. The new patch uses the debug_backtrace $options parameter to do this which makes execution faster. This also gives the developer an option to output the object/args elements in the backtrace by setting a variable.

So instead of:

$backtrace = debug_backtrace();

// Remove arguments/objects from the backtrace to make it lightweight.
foreach ($backtrace as $key => $value) {
  unset($backtrace[$key]['object']);
  unset($backtrace[$key]['args']);
}

We have:

$backtrace_options = variable_get('drupal_error_backtrace_options', DEBUG_BACKTRACE_IGNORE_ARGS);
$backtrace_limit = variable_get('drupal_error_backtrace_limit', 0);
$backtrace = debug_backtrace($backtrace_options, $backtrace_limit);

Dupe of #1158322: Add backtrace to all errors which has had much more activity on it.