SPV reader and writer support is now on master

[Ben Pfaff]

I just pushed support for SPV files to the master branch of PSPP.
This means a number of new features:

* There is a new program "pspp-output" that can convert .spv files
  into other formats, e.g. you can use it to produce text or PDF files
  from SPSS viewer files.

* The "pspp" program can now output to .spv files.

* PSPPIRE can now read and write .spv files.  The support for
  reading them is not refined enough (it simply dumps the to the
  output window), so it's not really documented yet.

I would appreciate experience reports, positive or negative.  The
main known limitation is that graphs are not yet supported (this
is actually a huge amount of work due to the way that SPSS
implements graphs).

Thanks,

Ben.