[Doxygen-develop] Do not discard unknow commands

[Hugo L. <hug...@op...>]

Hi;

I'm using doxygen to read the API documentaion of a third part
software, so I can't change the documentation inside the source code,
but doxygen give me a XML in their ouput and I can change it to
anything that I want, but there is a problem.

The documentation have some commands not recognized by doxygen, and
when doxygen find one of then it simply discard the comman characters
from the output, my patch tell doxygen to not discard unknow commands
characters.

I think that this patch do not affect the normal use of doxygen, the
current behaviour is undesired by the user, just as the new behaviour,
because the documentation must nto have any unknow commands.

Any comments?