I was going a bit crazy trying to figure out why tab completion in *shell* wasn't working for git add when I was trying to add a new file to my repo. Turns out pcomplete was only completing modified tracked files.This patch changes it so after git add it also completes untracked non-ignored files.

I believe I long ago signed a Copyright assignment to the Emacs project but I'm happy to do it again if that's still required. Cheers!