Generate info form of documentation using utf-8 encoding rather than
This change means we don't have to replace the entities defined in
math.ent by their written out (in ascii) equivalents for the info
case, and Table 3-4 looks correct (for the first time ever) in the generated
info form of our documentation.
Tested by: Alan W. Irwin <firstname.lastname@example.org> using the
cmake -DBUILD_DOC=ON option and the "info" target.