Revert "Try a third time to fix MSVC build after r234290"
Revert "Try a third time to fix MSVC build after r234290"

This reverts commit r234295 (and r234294 and r234292 before it).  I
removed the implicit conversion to `MDTuple*` r234326, so there's no
longer an ambiguity in `operator[]()`.

I think MSVC should accept the original code now...

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@234335 91177308-0d34-0410-b5e6-96231b3b80d8

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