typically bound to Shift-Tab. syscons produces ^]]Z for Shift-Tab, like
many VT100-like terminal (emulators). The plain xterm does not produce
this sequence, but ^I for both Tab and Shift-Tab.
PR: conf/162787
PR: bin/151229
Submitted by: Stefan Bethke <stb@lassitu.de>
Submitted by: Bruce Cran <bruce@cran.org.uk>
Approved by: cperciva
MFC after: 3 days
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