Make fixes and improvements

- Fix handling of precision in hex float formatting
- Enhance the cocmd interpreter for system() and popen()
- Manually ran the Lua unit tests, which are now passing
- Let stdio i/o operations happen when file is in error state
- We're now saving and restoring xmm in ftrace out of paranoia

libc/stdio/fwrite_unlocked.c

@@ -45,7 +45,7 @@ size_t fwrite_unlocked(const void *data, size_t stride, size_t count, FILE *f) {
   size_t n, m;
   const char *p;
   struct iovec iov[2];
-  if (f->state) {
+  if (!stride) {
     return 0;
   }
   if ((f->iomode & O_ACCMODE) == O_RDONLY) {