GladeXML::relative_file
string relative_file(string filename);
Creates an absolute filename from a relative one.
The new filename will be absolute to the directory of
the .glade file. If the filename
was absolute, it stays untouched.
Example: The .glade file is located at
/data/php/gtk/test.glade and you pass
"window.xpm" to this function, the result will be
/data/php/gtk/window.xpm.
