Simplify the code and avoid some allocations to improve performance.

I haven't checked the definition of RealType, but merging the output and
value variables might arguably affect precision. The unit tests still
seem to pass, however.

Tested by 2x upsampling a 10-band 5490x5490 float32 image on an Intel
Celeron J1900.

There is further room for improvement by eliding the remaining memory
allocations. A container like the small_vector from Boost might be
useful here, but we can't use that since it's not available in older
Boost versions.

before:
661.44s user 9.31s system 304% cpu 3:40.52 total
594.06s user 9.43s system 303% cpu 3:19.00 total
591.15s user 9.43s system 301% cpu 3:19.28 total

after:
443.42s user 10.48s system 294% cpu 2:34.00 total
443.11s user 9.87s system 309% cpu 2:26.27 total
448.50s user 10.50s system 311% cpu 2:27.52 total

Simplify the code and avoid some allocations to improve performance.

I haven't checked the definition of RealType, but merging the output and
value variables might arguably affect precision. The unit tests still
seem to pass, however.

Tested by 2x upsampling a 10-band 5490x5490 float32 image on an Intel
Celeron J1900.

There is further room for improvement by eliding the remaining memory
allocations. A container like the small_vector from Boost might be
useful here, but we can't use that since it's not available in older
Boost versions.

before:
661.44s user 9.31s system 304% cpu 3:40.52 total
594.06s user 9.43s system 303% cpu 3:19.00 total
591.15s user 9.43s system 301% cpu 3:19.28 total

after:
443.42s user 10.48s system 294% cpu 2:34.00 total
443.11s user 9.87s system 309% cpu 2:26.27 total
448.50s user 10.50s system 311% cpu 2:27.52 total

This reverts commit 4793d0f8, reversing
changes made to 88d2eae7.

BUG: Mantis-1300: don't use QDir::setCurrent() as it changes the system CWD and messes up with relative paths

Add ITK_OVERRIDE msotly in Monteverdi

save override in OTB (need to manually fix this after tidy)
  cd src/Modules ; grep -nR "override" * > ~/temporary/override_otb.txt
  cd ~/software
  python run-clang-tidy.py -checks=-*,modernize-use-override -header-filter=/home/grizonnetm/projets/otb/src/OTB/Modules/.*/.*/include/.* -j8 -fix -p ~/projets/otb/bin/release/OTB-clang3.8/ ~/projets/otb/src/OTB/Modules/*/*/src/*.cxx ~/projets/otb/src/OTB/Examples/*/*.cxx ~/projets/otb/src/OTB/Modules/*/*/test/*.cxx > ~/temporary/run-clang-tidy-log.txt
  #rename override with ITK macro ITK_OVERRIDE
  cd src/Modules
  find . -path ./ThirdParty -prune -o -type f -print -name "*.h" -o -name "*.txx" | xargs perl -pi -e 's/\ override/\ ITK_OVERRIDE/g'

This reverts commit c7fce23c.