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

third_party/sqlite3/os_unix.c

@@ -3531,16 +3531,6 @@ int sqlite3_sync_count = 0;
 int sqlite3_fullsync_count = 0;
 #endif
 
-/*
-** We do not trust systems to provide a working fdatasync().  Some do.
-** Others do no.  To be safe, we will stick with the (slightly slower)
-** fsync(). If you know that your system does support fdatasync() correctly,
-** then simply compile with -Dfdatasync=fdatasync or -DHAVE_FDATASYNC
-*/
-#if !defined(fdatasync) && !HAVE_FDATASYNC
-# define fdatasync fsync
-#endif
-
 /*
 ** Define HAVE_FULLFSYNC to 0 or 1 depending on whether or not
 ** the F_FULLFSYNC macro is defined.  F_FULLFSYNC is currently