including mml equation in the documentation

[ycollet at freesurf.fr]

Hello,

I think I have found a bug in the documentation building process.
I have a help page which includes a math formula. The math formula is
included in a .mml file which is in the same directory as the .xml files.
My native language is french, but I wrote the documentation in the en_US
directory.
The math formula is included as an informalequation and I make a reference
to the mml file.

When the documentation build process starts, the english help page is fine,
but there is a problem while building the french page because, the build
process doesn't find the .mml file in the fr directory. 
The .mml file in not copied from the en_US dir to the fr_FR dir.

But maybe my way to use the mml thing is wrong (in fact, it is partly wrong
because it works in english) ...

YC