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/calls/dup.c

@@ -34,7 +34,7 @@ int dup(int fd) {
   if (!IsWindows()) {
     fd2 = sys_dup(fd);
   } else {
-    fd2 = sys_dup_nt(fd, -1, 0);
+    fd2 = sys_dup_nt(fd, -1, 0, -1);
   }
   STRACE("%s(%d) → %d% m", "dup", fd, fd2);
   return fd2;