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/log/backtrace2.c

@@ -105,7 +105,7 @@ static int PrintBacktraceUsingAddr2line(int fd, const struct StackFrame *bp) {
     argv[i++] = buf + j;
     buf[j++] = '0';
     buf[j++] = 'x';
-    j += uint64toarray_radix16(addr - 1, buf + j) + 1;
+    j += uint64toarray_radix16(addr, buf + j) + 1;
   }
   argv[i++] = NULL;
   sigemptyset(&chldmask);