Total Syntheses of N^α- [1-(2-Acetamido-3-O-D-glucosyl)-D-propionyl-L-alanyl-D-α- and γ-glutamyl]-L-lysyl-D-alanyl-D-alanine, and Identity of the γ-Glutamyl Isomer with the Glycopeptide of a Bacterial Cell Wall Precursor