new nightly build system with binaries for many OSes

[Ben Pfaff]

I'm working on a new nightly build system.  It does the build,
runs the tests, and outputs the binaries on 5 different OSes.
Here's an example:
        http://benpfaff.org/~blp/pspp-porting/build91/

The "summary.html" files are probably the best way to view the
results.

I'm going to try to add a mingw build.
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I love the whooshing noise they make as they go by.
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