CellSens: fix off-by-ones in subresolution tile calculations (rebased onto develop)



This is the same as gh-1077 but rebased onto develop.

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This is likely to fail data test builds for the moment, as I'll need to update various configuration files.  The lowest 2-3 resolutions in each pyramid should now be slightly larger, and the ubiquitous black bands on the right-hand and lower edges should now be gone.

/cc @chris-allan