1866: small functionality change, better explanation.
Better 'tooltip' documention for different export formats.
Don't refer to Excel, say spreadsheet instead.
Only functionality change is standard CSV uses the rows.export_to_csv(..., represent=True) to make the output look like the on-screen grid representation.
The other formats are not changed, so both TSV and TSV with hidden columns do represent, and CSV with hidden columns does not (for speed)
rows.export_to_csv_file assumes the function field.represent takes only one argument, which was causing a ticket with virtua fields
missed a label
remove blank line
Merge pull request #379 from timrichardson/issues/1866

Issues/1866 (grid export): change csv export to use represent, no change to csv hidden cols or others.