Fix compilation problems in 'amp' plugin.

Four instances where 'default:' is at the end of a block replaced with
'default: break;' (reported by mscherer).

One typo where [j] should have been [1] (array out of bounds error).

Missing <unistd.h> includes for _exit(), and <string.h> for memcpy().

dll/amp/huffman.c

@@ -12,6 +12,8 @@
 #define HUFFMAN
 #include "huffman.h"
 
+#include <unistd.h>
+
 static inline unsigned int viewbits(int n)
 {
 unsigned int pos,ret_value;