Usermanual update
Merge pull request #714 from VictorLamoine/master

French translation of the entire usermanual
Define PATH_MAX as 4096 in case it is undefined.
Might fix build on Debian GNU/Hurd (i386)

https://buildd.debian.org/status/fetch.php?pkg=darktable&arch=hurd-i386&ver=1.4.2-1&stamp=1399195932