add wrapfd. improve fuzzer in makefile

--HG--
branch : fuzz

fuzz-wrapfd.h

@@ -0,0 +1,17 @@
+#ifndef FUZZ_WRAPFD_H
+#define FUZZ_WRAPFD_H
+
+#include "buffer.h"
+
+enum wrapfd_mode {
+    UNUSED = 0,
+    PLAIN,
+    INPROGRESS,
+    RANDOMIN,
+};
+
+void wrapfd_setup(uint32_t wrapseed);
+// doesn't take ownership of buf. buf is optional.
+void wrapfd_add(int fd, buffer *buf, enum wrapfd_mode mode);
+
+#endif // FUZZ_WRAPFD_H