compilation directives (cf. __APPLE__), were to rename the type
ColorTable to GmshColorTable and the function Palette to Palette1,
in order to avoid conflicts with Apple's QuickDraw.
Note that HFS is case-insensitive, which requires to have a fltk lib
name otherwise than libfltk.a (in the Mac version, the GL part is separate
anyway, so I've been using libfltk_base.a and libfltk_gl.a).

L'introduction d'une relaxation dans XYtoUV permet de resoudre pas mal de problemes (cf. bench/bugs/xy2uv