[Fixed for V0.42] Aysmmetric roof bitmaps

[linflas]

small bug found in editor :
i made 2 bitmaps for a sky, NS and EW.
i edit default wallset, then in roof tab, i assign NS to N and S, assign EW to E and W.
save the file and i see in txt file :
ROOF..........=(BITMAP_PLAINE_ROOF_NS,BITMAP_PLAINE_ROOF_EW,BITMAP_PLAINE_ROOF_EW,BITMAP_PLAINE_ROOF_EW)
instead of
ROOF..........=(BITMAP_PLAINE_ROOF_NS,BITMAP_PLAINE_ROOF_EW,BITMAP_PLAINE_ROOF_NS,BITMAP_PLAINE_ROOF_EW)

[George Gilbert]

Fixed for V0.42