Bug 10513: (follow-up) allow for multiline checkin alerts/messages

Bug 10513: (follow-up) allow for multiline checkin alerts/messages

This patch turns the form input for the checkin message to
a text area and uses the html_line_break Template Toolkit filter
to display it.

To test:

[1] Create or edit an item type.  Note that the checkin message
    field is a text area.
[2] Enter a checkin message with at least one line break.
[3] In the item types administration page, note that the checkin
    message is displayed with the line break.
[4] Return an item of the item type modified in step 1.  Verify
    that the displayed checkin message includes the line break.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>