Clean up texinfo files

Clean up texinfo files

Fix up the com_err.texinfo file so it will produce a valid printed
output, by cleaning up some errors in the texinfo file, and updating
texinfo.tex to be consistent with the version in the doc subdirectory.

Also add rules so we can generate pdf and ps files from
com_err.texinfo and libext2fs.texinfo.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>