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This completes the changes in the documentation.

- icetUnsafeStateGet now returns const.
- new ICET_COLLECT_TIME timing metric.
- ICET_COLLECT_IMAGES option.
- ICET_VALID_PIXELS_* state variables.
- Matrix helper functions.
- Input array for icetSendRecvLargeMessages became const.
- Background correction in strategies.

- ICET_MAGIC_K and ICET_MAX_IMAGE_SPLIT CMake, env, & IceT variables.
- icetCompressedCompressedComposite.
- Sparse image copy and split.
- Image interlacing.
- Image equal functions.
- icetDecompressSubImage.
- icetRenderTransferSparseImages.
- Sparse image null functions.

Now accepts and returns sparse images.  Also no longer collects image
pieces.

- Radix-k and its selection.
- icetAddTiles raises ICET_INVALID_VALUE for 0-pixel tile.
- icetFindRankInGroup and icetFindMyRankInGroup.
- New communication functions.
- Sequential strategy skips some collective operations.
- icetImageAssignBuffer and icetSparseImageAssignBuffer.
- ICET_SIZE_TYPE.
- ICET_IN_PLACE_COLLECT.

All the interesting changes on Release were already in master.  This
merge is basically for safety sake.

Use it to correct some background correction problems with blank tiles.

Makes us more assured that a failure will actually be reported as such.

Previously background correct only happened on display processes after
the image was collected.  Now we encourage distributed correction before
collection.  In this case, it was wrong to not correct on non-display
processes.

This also enables background correction in the sequential and reduce
strategies.

Created new state variables to capture the final background and a
flag whether the correction is really necessary.  Also moved the
background correct function to image.c, but it is not used yet.

The method did an all gather that collected on each process masks for
all processes for what processes it gets messages.  This takes n^2
where n is the number of processes.  For large numbers of processes,
that gets really big.  This change uses all to all to collect only
which messages the local process gets.

Previously, debugging logs were shown in tests and had to be shut
off.  This lead to very verbose output that hardly ever helped much.
Now the behavior is the opposite.  Debug logs are not shown by default
but can be turned on with a flag (assuming compiled in debug mode).

Messages that print everywhere should also report from what process
they come from.