Enables activity masking by default
Update DCT tests to account for OD_COEFF_SHIFT.

This also changes the quantization bias tests to actually round the
 quantization decisions instead of truncating towards 0.

The interesting result here is that with OD_COEFF_SHIFT == 4, we
 get bit-exact matches between the integer and float iDCTs on these
 particular tests (after undoing the scaling and rounding the
 output back to integers).
With OD_COEFF_SHIFT == 3, 4x4 and 8x8 are still exact matches, and
 16x16 still passes IEEE 1180.
With OD_COEFF_SHIFT == 2, 4x4 and 8x8 still pass IEEE 1180, but
 16x16 starts to fail the MSE tests.

However, we're using the test thresholds for 8x8 at all transform
 sizes, since IEEE 1180 was only ever defined for 8x8.
These might need some tweaking in a more serious test (though in
 which direction I couldn't answer without doing more thinking than
 I've done on the subject).

N.B., using the technique we're currently using to round the final
 pixel values to integers after the iDCT introduces the majority of
 the transform bias (approximately 0.5/(1<<OD_COEFF_SHIFT)).
Since those pixel values are not really signed (or rather, they
 might have an arbitrary DC shift which could give the whole image
 whichever sign you like), the only solution I see to that is to
 use round-to-even.
Fix the coding style in the DCTs.

This was bad enough that I needed to do something about it.
Remove the DCT basis scaling from the tests.

Now that we're committed to having uniform (and indeed orthonormal)
 scaling, there is no need to support the correction factors needed
 by a non-orthonormal DCT.
DCT test refactor step 1: Merge float iDCTs.

There's too much copy-and-paste code in the DCT tests.
This is the first step in eliminating the redundancy.
DCT test refactor step 3: Merge IEEE 1180 block test.
DCT test refactor step 4: Merge IEEE 1180 test driver.
DCT test refactor step 5: Merge MSE computations.

The 4x4 test only computes fDCT bases, not iDCT, for no good
 reason.
That will be fixed when the driver is merged.
DCT test refactor step 6: Merge bias checks.
DCT test refactor step 7: Merge top-level driver.
Add tests for overflow, and fix some DCT overflows.

This runs pixels through the transform designed to achieve the
 minimum and maximum value for each coefficient, and checks for
 overflow before each multiply.
The multiply constants have been adjusted to eliminate overflow
 each place it occurred in these tests.

Technically, we should be choosing pixel values to minimize or
 maximize the intermediate value being multiplied, but doing that
 is a lot more complicated.
This should at least solve the worst of the problems.
Move newdct.c to dct.c.

I think it's been long enough that we're not likely to switch back
 to the old factorizations anymore.
Add an exit code to the DCT tests.

This lets us know when they've failed so we can stick them in an
 automated test.
Add the DCT tests to the test suite.

Now that we have some hard conditions we can check, no reason not
 to check them always.
Also fixes a couple of warnings needed to get them to build with
 the unix Makefile.
Fix linking of dcttest with assertions enabled.

I'd done this for the unix Makefile, but not autotools, apparently.
r=bustage
Removed signed overflow from IEEE 1180 DCT tests.

Well-defined tests are a plus.