Added expr, from Edward Betts <edward@debian.org>, with some fixups
and docs added by me.
 -Erik
diff --git a/busybox.def.h b/busybox.def.h
index 3ad118d..f88851a 100644
--- a/busybox.def.h
+++ b/busybox.def.h
@@ -27,6 +27,7 @@
 #define BB_DU
 #define BB_DUMPKMAP
 #define BB_ECHO
+#define BB_EXPR
 #define BB_FBSET
 #define BB_FDFLUSH
 #define BB_FIND