First french translation!

[marsgui]

This pull request just to let you know the progress. Things to do:

• Translate bookinfo, abstract, colophon, legal notices
• Translate the missing footnotes (many still in english)
• Translate the indexterms (big deal: around 700 strings)
• Translate the other missing strings (some tites, and a table)
• Review and fix the translations

[petterreinholdtsen]

I've added build rules for the French version. I had to clean up the .po file to get the PDF built.