Fixed warnings with gcc option "-Wwrite-strings".

include/bitmaps/wine.xpm

diff --git a/include/bitmaps/wine.xpm b/include/bitmaps/wine.xpm
index 613f921..85e34f8 100644
--- a/include/bitmaps/wine.xpm
+++ b/include/bitmaps/wine.xpm
@@ -1,5 +1,5 @@
 /* XPM */
-static char * wine_xpm[] = {
+static const char * wine_xpm[] = {
 "48 48 159 2",
 "  	c None",
 ". 	c #010101",