Exporting a CSV on a form with a textarea that contains a line break makes the CSV go to a new row

[benkeen]

When you have a form that contains a textarea there's an issue with the CSV exporter if a submission includes a line break (return/enter) in the textarea. It causes the submission to go to a new row at the line break.
I'm not sure if CSV supports a line break, so the best possible solution that I can think of is to update this module to convert a line break into a space before serving up the file.

Steps to reproduce:

1. Create a form with a textarea
2. Enter a submission, and have the textarea contain multiple lines (using enter/return to go to a new line)
3. Export submissions as a CSV