Fix timedelta scalar multiplication

This fixes a bug in elementwiseScalarMultiplyTimeDelta introduced in !5 (merged): in the original implementation, we had something like scaled_td += lambda * base_td but f3844207 replaced it with something like scaled_td = lambda * base_td.

The bug was the reason why we urgently had to introduce d7586b2b into the master right before the first open-source release of ICON (several Buildbot tests on the DWD machine kept failing). That commit was dropped and the master was updated with force-push.

added 16 commits

• 10dea214...4823d787 - 15 commits from branch master
• 5ab55562 - Fix timedelta scalar multiplication

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For the record: ICON does not fail the Buildbot tests on DWD machine with these changes anymore (see here). But there is one more issue to investigate before we merge this (see here).

mentioned in merge request !19 (merged)

added 6 commits

• 5ab55562...15ab482b - 5 commits from branch master
• 112f69a4 - Fix timedelta scalar multiplication

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merged