Question 2: Here's the full original quote: "Out, damned spot! Out, I say!—One, two. Why, then, ’tis time to do ’t. Hell is murky!—Fie, my lord, fie! A soldier, and afeard? What need we fear who knows it, when none can call our power to account?—Yet who would have thought the old man to have had so much blood in him."
In this scene, Lady Macbeth is feeling guilt for crimes she committed earlier in the play. She believes she sees blood and cannot remove it. "Out, damned spot!" is actually one of the most famous lines in the play.
In the book, however, the man is quoting Shakespeare ironically. He does not believe the boy could possibly have spit into twenty cups.
Question 1: "neat" is an older word for "cool" or "interesting." So she is saying that normally Mason was not very interesting, but because of the way Mr Clayton is talking about him, Mason almost seems cool or interesting.