CSV file path corrupted (not URL encoded) when starting CSV import wizard

To reproduce:

1. Go to the CSV import page (/secure/admin/views/CsvImporter!default.jspa)
2. Enter "foo+bar" into the "CSV Import file" field.
3. Click the "Import Wizard" link

The "CSV Import file" field on the next page will contain "foo bar", indicating that the filename has not been URL encoded during the transition.