Add afl fuzzing helpers.

tools/afl/aggregate_cases.sh

@@ -0,0 +1,13 @@
+set -eux
+
+n=0
+for tc in $(echo ./fuzz_out/$1/*/hangs/* ./fuzz_out/$1/*/crashes/*)
+do
+  if ! test -e $tc
+  then
+    continue
+  fi
+  mkdir -p ./fuzz_out/$1_aggregated/
+  cp "$tc" $(printf "./fuzz_out/$1_aggregated/$1-%04d.test" $n)
+  n=$((n + 1))
+done