error.phtml: fixed erasing of HTML output
fixes
Debugger::_exceptionHandler sends header ContentType: text/html; charset=utf-8
Debugger::_exceptionHandler only tries to log errors occurred in $onFatalError
Debugger::_exceptionHandler() prints error when log() throws exception
Debugger::enable(): exit() replaced with _exceptionHandler()
Logger: throws exception when is unable to write to log file
Debugger::enable() checks whether log directory exists and is absolute (BC break, path must be absolute)