Step 1 in fixing 1859: this stops the crashing, but virtual fields are not exported
step 2 of fixing export from grids when there are virtual fields. Note export hidden columns includes all table fields and any virtual fields which are displayed, but it does not pick up virtual fields which are not displayed.
when exporting hidden columns, pick up all virtual fields, even those not on display.
fixed comment
Minor usability improvement to grid search widget
changed the button "New" to "Add" and added a title attribute (view on hover) explaining what this button does
Merge pull request #371 from timrichardson/issues/1859

Issues/1859 export from grid fails when virtual fields are present
Merge pull request #372 from timrichardson/search_widget_button_label_change

Minor usability improvement to grid search widget