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/dup2.c

@@ -38,7 +38,7 @@ int dup2(int oldfd, int newfd) {
   } else if (!IsWindows()) {
     rc = sys_dup3(oldfd, newfd, 0);
   } else {
-    rc = sys_dup_nt(oldfd, newfd, 0);
+    rc = sys_dup_nt(oldfd, newfd, 0, -1);
   }
   STRACE("dup2(%d, %d) → %d% m", oldfd, newfd, rc);
   return rc;