Code review comment for lp://staging/~nmb/bzr/fix-496917

This adds better feedback to the unshelve command. When it reads the shelf, it prints out which shelf it is using and then if it does delete the shelf, it prints that it is deleting the shelf. With the four action options to unshelve, this covers all of the bases fairly well, I think. New shell-like tests in bzrlib/tests/blackbox/test_shelf_ui.py.