[International / GSM] How to unroot and relock the galaxy nexus on a mac?


Could some one please explain, step by step, how to unroot and relock the bootloader on a mac?

I am currently rooted and unlocked, which was done on my mac. I had found detailed instructions which guided me through the process. I am looking forward to flashing roms on my GN. Before I start flashing roms, I need to learn how return to stock, using my mac. Can anyone share the step by step instructions or direct me to were I can get them?

Should someone be patient enough to explain, I would appreciate if you would differentiate when to use the enter key or the space key? As a noob to using terminal commands, those that are more experienced ,often assume that we will understand how they get from one line of code to the next. That has had me pulling the hair right out of my nooby head trying to figure out if I missed or added a step to many.

Thank You