Improve Checks for Flushing and Overrun

[phillipjohnston]

Right now, we do this check per-character, which is quite inefficient:

	virtual void log_add_char_to_buffer(char c)
	{
		if(auto_flush() && (internal_size() == internal_capacity()))
		{
			flush();
		}
		else if (internal_size() == internal_capacity())
		{
			overrun_occurred_ = true;
		}

		log_putc(c);
	}

Ideally we'd check for the full contents of the string to be added to the log, splitting earlier than the character level. Perhaps this occurs in print()?