progress with SPO files

[Ben Pfaff]

I've made some progress figuring out the SPO file format (the format
used for SPSS 15 and earlier output files). As a first step, I added
code that can parse TLO files, a simpler but closely related format
that SPSS 15 and earlier use for TableLooks:
https://git.savannah.gnu.org/cgit/pspp.git/commit/?id=24e84c14af8ac6dc897344104e756c8820f9a031

I didn't report it here at the time, but a few weeks ago I added
support for the STT files that SPSS 16 and later use for TableLooks.
For now, you can use them on the new --table-look option to
pspp-output. I intend to add support for them in PSPP itself with SET
TLOOK. Probably should support them in PSPPIRE too.