Improve debug of boot on real hardware

Debugging on real hardware is difficult, as the relevant boot messages are limited, and many people want to debug their boot but don't know where to start. Here are some suggestions, and other strategies are welcome.

• Have a "debug boot" option, which greatly increases the amount of log messages printed. According to bjorn3, this is a supported feature of boot in general, but I am not certain if there is an environment variable or a command line arg that is used to flag the increased logging
• Wait for a key press or other event before clearing the screen (perhaps only in "debug boot" mode) before enabling the GUI or running getty/login.
• Add a command line arg that can be invoked by init.rc or the init.d file.