Preview broken for field_timestamp

Some fieldtypes, timestamp in particular, don't hold a value in $node->$fieldname until after submit. This means they cannot be previewed. This is currently the case w/ date fields--date fields do not show up in preview mode.

There are two things needed to fix this: one in flexinode.module and one in field_timestamp itself.

The patch which fixes flexinode.module is attached. It simply adds an exception for the case when $node->preview is true.

The patch to field_timestamp will follow. It uses $node->preview to determine how to properly format the date field.