add more comments

array/iarray_free.c

@@ -1,12 +1,18 @@
 #include <stdlib.h>
+#ifndef __MINGW32__
 #include <sys/mman.h>
+#endif
 #include <unistd.h>
 #include "iarray.h"
 
 static void freechain(iarray_page* p,size_t pagesize) {
   while (p) {
     iarray_page* n=p->next;
+#ifdef __MINGW32__
+    free(p);
+#else
     munmap(p,pagesize);
+#endif
     p=n;
   }
 }