nested @ignore does not work

[Gavin Smith]

Not a big deal but I noticed that nested @ignore does not work with
texi2any, although it does work with texinfo.tex.  For example:

@ignore
@titlepage 
@title Texinfo
@subtitle The GNU Documentation Format
@subtitle for Texinfo version @value{VERSION}, @value{UPDATED}

@author Robert J. Chassell
@author Richard M. Stallman

@page
@vskip 0pt plus 1filll
@insertcopying

@sp 1
Published by the Free Software Foundation @*
51 Franklin St, Fifth Floor @*
Boston, MA 02110-1301 @*
USA @*
ISBN 1-882114-67-1 @c for version 4.0, September 1999.
@c ISBN 1-882114-65-5 is for version 3.12, March 1998.
@c ISBN 1-882114-64-7 is for edition 2.24 of November 1996.
@c ISBN 1-882114-63-9 is for edition 2.20 of 28 February 1995.

@ignore
@sp 1
Cover art by Etienne Suvasa.
@end ignore
@end titlepage
@end ignore

With texi2any there are errors:
texinfo.texi:93: unmatched `@end titlepage'
texinfo.texi:94: unmatched `@end ignore'

However, it processes as expected with texinfo.tex.

I don't have a strong preference as to whether nested @ignore should
work or not but it should be consistent between the two processors.
I think we should take whichever is the easiest to implement.

In texinfo.tex, @ignore is implemented in exactly the same way
as ignored conditionals, such as @ifxml, which do nest (at least
in part - I haven't thoroughly tested different combinations).

However, if it would be any effort at all to change texi2any then
I expect it would be straightforward to change texinfo.tex to terminate
the @ignore at the first "@end ignore" encountered.