[mantisbt-lang] French strings (8859-15 encoded)

[Maurice A. L. <leb...@co...>]

Herewith my draft translation of the French strings file with 8859-15 
encoding.

I have added comments to a few lines for further research where the 
functionality was not completely clear to me.

New strings based on the English strings file sent by Victor were 
added to the 1.1 French (8859-15) file distributed with the 1.1.0rc1 
release package.

Regards,

Maurice