Configuration option to define wether to follows GNU sed's behaviour

or the posix standard.
Put the cleanup code back the way it was.

testsuite/sed/sed-append-next-line-gnu

@@ -0,0 +1,14 @@
+# FEATURE: CONFIG_FEATURE_SED_GNU_COMPATABILITY
+busybox sed 'N;p'>output <<EOF
+a
+b
+c
+EOF
+cmp -s output - <<EOF
+a
+b
+a
+b
+c
+
+EOF