The blues referred to above, sung by Fred McDowell, and the Sonny Terry and Brownie McGhee song, are versions of <> by Johnny Temple and Royston Mayoh. I'll post the lyric later when I've found the record. I seem to remember that Sonny Terry would sing this solo, with harmonica breaks between lines, while Brownie drank a cup of tea.

It may be of interest that the Leo Kottke version of the Paul Siebel song is performed in C tuning, ie CGCGCE. I believe that Ms Raitt used this tuning also, as it is amenable to bottleneck work.