Allow combinations with Backspace

XN_ANY_MOD makes that any combination of backspace will return always
DEL. This patch lets to X to decide which value returns.

config.def.h

@@ -259,7 +259,7 @@ static Key key[] = {
 	{ XK_Delete,        ShiftMask,      "\033[3;2~",    +1,    0,    0},
 	{ XK_Delete,        XK_ANY_MOD,     "\033[P",       -1,    0,    0},
 	{ XK_Delete,        XK_ANY_MOD,     "\033[3~",      +1,    0,    0},
-	{ XK_BackSpace,     XK_ANY_MOD,     "\177",          0,    0,    0},
+	{ XK_BackSpace,     XK_NO_MOD,      "\177",          0,    0,    0},
 	{ XK_Home,          ShiftMask,      "\033[2J",       0,   -1,    0},
 	{ XK_Home,          ShiftMask,      "\033[1;2H",     0,   +1,    0},
 	{ XK_Home,          XK_ANY_MOD,     "\033[H",        0,   -1,    0},