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[ks905383]

Minor fixes

• Exporting to files or datasets no longer adds a superfluous variable named after the first variable in the input dataset.
• Exporting to geodataframe now fails loudly (with tips for a workaround) instead of silently when multiple variables are exported
• Docs for exporting improved.
• silent=True now works for exports to files.

Under the hood

Added ~ a dozen tests to make exporting and aux functions more robust.