makeinfo 5.0 is 34x slower when building Emacs info

[Paul Eggert]

Running Emacs's 'make info' takes 6.5 seconds with texinfo 4.13,
but 224 seconds with texinfo 5.0, a factor of 34 slowdown.
It's now quite a wait for me to run 'make info', and this
is an annoyance -- can this be sped up?

My environment is Fedora 17 x86-64 and an
AMD Phenom II X4 910e processor.

To reproduce the problem, grab this tarball:

ftp://alpha.gnu.org/gnu/emacs/pretest/emacs-24.2.93.tar.xz

Extract it, then run the following shell commands:

cd emacs-24.2.93
./configure
rm $(find . -name '*.info')
make info MAKEINFO=/path/to/makeinfo-4.13/bin/makeinfo
rm $(find . -name '*.info')
make info MAKEINFO=/path/to/makeinfo-5.0/bin/makeinfo

The first 'make' runs many times faster than the second.