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/sock/winsockblock.c

@@ -30,6 +30,11 @@ textwindows int64_t __winsockblock(int64_t fh, unsigned eventbit, int64_t rc) {
   if (WSAGetLastError() != EWOULDBLOCK) return __winsockerr();
   eh = WSACreateEvent();
   bzero(&ev, sizeof(ev));
+  /* The proper way to reset the state of an event object used with the
+     WSAEventSelect function is to pass the handle of the event object
+     to the WSAEnumNetworkEvents function in the hEventObject parameter.
+     This will reset the event object and adjust the status of active FD
+     events on the socket in an atomic fashion. -- MSDN */
   if (WSAEventSelect(fh, eh, 1u << eventbit) != -1 &&
       WSAEnumNetworkEvents(fh, eh, &ev) != -1) {
     if (!ev.iErrorCode[eventbit]) {