Update of texinfo.tex, and cherry-picks in stable/2.20

[John Mandereau]

Hi folks,

As suggested by Werner on February 8th in "Please test GUB" thread, we
should update tex/texinfo.tex in our sources from Texinfo git repo. Is
there any objection to applying this change on both staging and
stable/2.20 branches without the usual review process?


I also have another request for stable/2.20: could we cherry-pick the
following commits from master?

88633ac Issue 5469/2: Add `TEX` environemnt variable for texi2pdf
e757c64 Issue 5469/1: Tweak wrapped lines
002382c Issue 5463: Fix dblatex uses xetex backend

Best,
John