[sample patch]: FileName class

[Angus Leeming]

I remember having a rant sometime ago about the need for something better 
than our current handling of file names. My proposal was to have a helper 
class that would enable us to 'do the right thing' when reading/writing the 
buffer to file:

class FileName {
public:
        FileName();
        /** \param abs_filename the name of the path with full path.
            \param save_abs_path should the file name be stored in the
            LyX file as an absolute path or relative to the buffer?
         */
        FileName(string const & abs_filename, bool save_abs_path = true);

        bool empty() const { return name_.empty(); }

        string const absFilename() const { return name_; }
        void absFilename(string const abs_filename);

        bool saveAbsPath() const { return save_abs_path_; }
        void saveAbsPath(bool);
private:
        string name_;
        bool save_abs_path_;
};

Internally we use FileName::absFilename() but we check 
FileName::saveAbsPath() when reading/writing to file.

The attached patch implements this and uses it for the graphics inset. (Also 
removes a couple of #warnings as the code is fixed properly.)

Do people think this is a clean solution? Should I move the class into its 
own files rather than putting it in support/filetools.[Ch]?

Comments please.

-- 
Angus