makeinfo fd leak? and gendocs.sh exit status bug

[Eric Blake]

I noticed this when running the new gendocs.sh on the Autoconf tree on cygwin; 
when I tried the same process on Linux, there was no problem.  Since cygwin 
enforces a smaller cap on number of open fd, I suspect that makeinfo might have 
an fd leak, although I have not investigated further at this point.  I 
reproduced this by using 'gmake web-manual' using the latest autoconf.git.

Generating html by node... (env LANG= LC_MESSAGES= LC_ALL= LANGUAGE= makeinfo --
html -o autoconf.html  "/home/eblake/autoconf/doc/autoconf.texi")
/home/eblake/autoconf/doc/autoconf.html/m4_005ffatal.html: Too many open files

On both machines, I used:
$ makeinfo --version | head -n1
makeinfo (GNU texinfo) 4.8

Meanwhile, even after that message, gendocs.sh ran to completion with an exit 
status of 0, so someone is failing to propogate the error status properly.

-- 
Eric Blake