bug#11011: Binding S-TAB

[Drew Adams]

> Btw, binding <S-tab> would have also done TRT in that use case.

Yes.  IIUC, to be more exact, <backtab> takes care of two cases:
<S-tab> and <S-iso-lefttab>.

To get the effect of <backtab> for Emacs prior to 22 you had to
bind both of those keys ([S-tab] and [S-iso-lefttab]).