intfbin/msspwglue: make it so we can field-split in one invocation
intfbin/casa-script: rewrite to possibly be useful

I wasn't using the previous incarnation anywhere because it was not, in fact,
very useful at all. See header comments in new version for how it works.
intfbin/casa-importevla: command-line tool for this

Now that we have a working casa-script, provide command-line access to importevla
with automatic configuration the way we want. I don't think it can be accessed
on the Unix CLI otherwise, and the prospect of reimplementing the online-flags
code in tasklib was too gross.