This was writing time_t to disk. Worse, the time_t member was at an
unaligned offset in the structure in question, so after the time_t
change the structure layout depended on compiler-inserted structure
padding. This gives three legacy formats: one with 32-bit time, one
with 64-bit time, and one with 64-bit time and 4 bytes of structure
padding.
And of course the file didn't have a header or version coding or
anything.
The new code writes a structure of well-defined size that should not
receive unexpected padding, and gives the file a header and version
number. It reads that format and any of the three legacy formats,
figuring out which one it's dealing with by inspecting the file
contents. For good measure, it also now handles opposite-endian files,
doesn't bail out unceremoniously unless necessary, and won't croak if
the file is corrupt and e.g. contains unterminated strings.
(Was it worth going to this length? Maybe not. But it didn't seem
right to just leave it, and it's not clear where to stop halfway.)
