change length or size specifiers in APIs from int to long

add array API (http://cr.yp.to/lib/array.html)

array/array_get.c

@@ -0,0 +1,30 @@
+#ifdef __dietlibc__
+#include <sys/cdefs.h>
+#else
+#define __likely(x) x
+#define __unlikely(x) x
+#endif
+#include "safemult.h"
+#include "array.h"
+
+#if 0
+      static array x;
+      t *p;
+      int64 pos;
+
+      p = array_get(&x,sizeof(t),pos);
+
+   array_get is similar to array_allocate, but it does not allocate any
+   extra bytes, and it does not initialize any extra bytes. It
+   returns 0 if x is unallocated, for example, or if fewer than
+   (pos+1)*sizeof(t) bytes are initialized.
+#endif
+
+void* array_get(array* x,uint64 membersize,int64 pos) {
+  uint64 wanted;
+  if (__unlikely(pos+1<1)) return 0;
+  if (__unlikely(umult64(membersize,pos,&wanted))) return 0;
+
+  if (__unlikely(wanted > x->allocated)) return 0;
+  return x->p+pos*membersize;
+}