Always save a key/value hash of the selected value(s). However, if the field
does not have the multivalue configuration setting, then retrieve just the
key with the to_php() function. to_database(), however, will always return a
JSON string with the value(s) formatted as a hash array.

This allows for subclasses to define how the choice is formatted.
Split ticket status states into public and private

Previously, the characters would be removed and the data would be considered
empty which would bypass validation and clear the phone number on save
rather than triggering a validation error.

Also add some logic to the POT builder to warn about incorrect arguments to
the __() function and friends as well as warn about _() usage.

Add multiselect  option to selection and choices fields.

Instead, previously, a maxlength of zero effectively disabled the field,
because it prevented any user input into the field.

The ThreadEntryWidget has a potential cross site scripting (XSS)
vulnerability if data was posted directly to the page hosting the widget

Vulnerable URLs:
view.php, open.php, scp/open.php, scp/tickets.php

The content received in the HTTP POST is now correctly escaped when it is
echoed back to the user agent.

The `id` needs to be changed for the new clone in order for the POST data to
line up with with new field

Sanitize textarea content on export

This make writing new backends (such as LDAP) easier and less copy+pasting
is required.

Otherwise, it might be possible for a forwarded email to accidentally
contain a ticket link, with which a sinister individual might be able to use
to register for account on behalf of the original client, and, at the same
time, be able to change the user's email address to his/her own.

Priority field and custom list fields have a prompt value (shows up only for
drop-down widget). And the short and long answer fields have a placeholder
configuration item.

Allow the administrator to enter a prompt to be shown in the choices
drop-down for choice fields. Also add the option of selecting a default
value from the list initially rather than displaying a prompt.

This is necessary because the system depends ticket priority to sort and
display ticket data.

Also add in the user email address after the user name.

This patch also adds an ::export() method to the FormField() class which
allows a field to define how the data should be formatted when exported.

Fixes #390