Using @documentencoding UTF-8 slows makeinfo down by nearly 25%

[Gavin Smith]

When working on character encoding issues for the Texinfo parser I
found that the run time of makeinfo would be slower when a UTF-8
encoding was used.

Running "makeinfo elisp.texi" (the Emacs Lisp manual) runs in about 49
seconds on my computer.

When I comment out the "@documentencoding UTF-8" line this comes down
to about 40 seconds.

I haven't found a way to make using UTF-8 as fast as not. I expect the
speed difference is due to the way Perl processes UTF-8 strings
internally.