add iob_free and man page for iob_reset.

check in some windoze compat crap (still does not compile through for
windoze)

buffer/errmsg_warn.c

@@ -1,6 +1,16 @@
 #include <stdarg.h>
 #include <sys/types.h>
+#ifdef __MINGW32__
+#include "windows.h"
+#include <unistd.h>
+
+struct iovec {
+  LPCVOID iov_base;
+  DWORD iov_len;
+};
+#else
 #include <sys/uio.h>
+#endif
 #include "errmsg.h"
 #include "str.h"
 
@@ -10,6 +20,15 @@ void errmsg_warn(const char* message, ...) {
   struct iovec x[23];
   va_list a;
   va_start(a,message);
+#ifdef __MINGW32__
+  {
+    int i,j;
+    j=errmsg_cvt(x,message,a);
+    for (i=0; i<j; ++i)
+      write(2,x[i].iov_base,x[i].iov_len);
+  }
+#else
   writev(2,x,errmsg_cvt(x,message,a));
+#endif
   va_end(a);
 }