Improve synchronization

- Fix bugs in kDos2Errno definition
- malloc() should now be thread safe
- Fix bug in rollup.com header generator
- Fix open(O_APPEND) on the New Technology
- Fix select() on the New Technology and test it
- Work towards refactoring i/o for thread safety
- Socket reads and writes on NT now poll for signals
- Work towards i/o completion ports on the New Technology
- Make read() and write() intermittently check for signals
- Blinkenlights keyboard i/o so much better on NT w/ poll()
- You can now poll() files and sockets at the same time on NT
- Fix bug in appendr() that manifests with dlmalloc footers off

libc/zipos/open.c

@@ -124,12 +124,13 @@ static int __zipos_load(struct Zipos *zipos, size_t cf, unsigned flags,
     h->mem = NULL;
   }
   if (h->mem) {
-    if ((fd = IsWindows() ? __reservefd() : dup(2)) != -1) {
+    if ((fd = IsWindows() ? __reservefd(-1) : dup(2)) != -1) {
       if (__ensurefds(fd) != -1) {
         h->handle = g_fds.p[fd].handle;
         g_fds.p[fd].kind = kFdZip;
         g_fds.p[fd].handle = (intptr_t)h;
         g_fds.p[fd].flags = flags | O_CLOEXEC;
+        g_fds.p[fd].mode = mode;
         return fd;
       }
       close(fd);