Make redbean StoreAsset() work better

- Better UBSAN error messages
- POSIX Advisory Locks polyfills
- Move redbean manual to /.help.txt
- System call memory safety in ASAN mode
- Character classification now does UNICODE

libc/nt/enum/lockfile.h

@@ -0,0 +1,7 @@
+#ifndef COSMOPOLITAN_LIBC_NT_ENUM_LOCKFILE_H_
+#define COSMOPOLITAN_LIBC_NT_ENUM_LOCKFILE_H_
+
+#define kNtLockfileFailImmediately 1
+#define kNtLockfileExclusiveLock   2
+
+#endif /* COSMOPOLITAN_LIBC_NT_ENUM_LOCKFILE_H_ */