calcs/base:

Fixed exported filename collection in the base `export` method.
export/risk:

Fixed a couple of risk export functions, where the `dest` parameter (a
path or file-like) was being passed as a keyword arg--which was not
appropriate, since this is a positional argument and makes refactoring/
renaming error-prone.
tests/export/risk_test:

Fixed a few broken tests, due to some slight changes in the calls to
the various output serializers.