intel: Add regression tests for batch decode.

The .batch was generated using the dump-a-batch branch of

git://people.freedesktop.org/~anholt/mesa

using glxgears on gen7 hardware, using INTEL_DEVID_OVERRIDE for
non-gen7 (this means that offsets in the buffers for non-gen7 are 0!).
The .ref was generated by:

./test_decode tests/gen7-3d.batch -dump.

The .sh exists because you can't supply arguments to tests using the
simple automake tests driver.  Something reasonable could be done
using automake's parallel-tests driver (in fact, a previous version of
the patch did that), but I was concerned that:

1) The parallel-tests driver is documented to be unstable -- they may
   change interfaces on us later.
2) The parallel-tests driver hides the output of tests in .log files
   scattered all over the tree, which was ugly and more painful to
   work with.

v2: Actually add the batch files, add a .gitignore for the *-new.txt
    files added after failures, and fix failure mode for undetected
    chipset name.
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> (v1)