Function: smarty_make_timestamp
Purpose: used by other smarty functions to make a timestamp from a string.

• author: Monte Ohrt <at ohrt dot com monte at ohrt dot com>
• usedby: smarty_modifier_date_format()
• usedby: smarty_function_html_select_time()

• DateTime|int|string $string: date object, timestamp or string that can be converted using strtotime()