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/log/die.c

@@ -58,7 +58,7 @@ relegated wontreturn void __die(void) {
     _Exitr(77);
   } else if (owner == me) {
     kprintf("die failed while dying\n");
-    _Exitr(78);
+    _Exitr(79);
   } else {
     _Exit1(79);
   }