Strip unnecessary details in error logs

[dvz]

The error logs may contain entries unrelated to problem origins.

• The function added via Add separate callback function for set_error_handler() #4440 results in an additional call (internal to the error handler) logged as:

  #0  errorHandler->error() called at [/inc/class_error.php:153]
  

  The $strip argument in calls to errorHandler:generate_backtrace() within the class should be adjusted so that the first entry references the path and line number of a point of interest:

  #0  errorHandler->error_callback() called at [origin of the problem]
  

• The errorHandler::email_error() method calls the debug_print_backtrace() function directly, which may include unnecessary entries, and additionally include arguments values due to a missing DEBUG_BACKTRACE_IGNORE_ARGS flag.

  cf.

  mybb/inc/class_error.php

  Line 752 in 89ba6fd

  $trace = debug_backtrace(1<<1 /* DEBUG_BACKTRACE_IGNORE_ARGS */);