- Fix an error-path leak of memory and a dentry in load_elf_binary()
  (spotted by Oleg Drokin).

- Tidy up the handling of bad executable images: return -ENOEXEC rather
  than 0.  (We've committed suicide anyway, so probably nobody gets to see
  this).

- Fix up the logic in load_aout_interp().  It gets itself all set up to
  return -ENOEXEC but there is in fact no path by which it can do this.  Just
  return ~0UL on errors, like load_elf_interp().