find and replace all periods that are not followed by punctuation or a space : <p>I'm trying to format user input using PHP, and am frequently running into issues where there are not spaces between sentences (i.e. after a closing period).  This creates problems, as this user input gets professionally printed.  If we miss these during a manual QC process, it costs the company money, as it has to be fixed and reprinted.</p>

<p>I need to develop a way to search for all periods in a given text string, determine if it's immediately followed by a letter or number, and if so, insert a space after the period.  If the period is followed by other punctuation (i.e. a quotation mark, another period as in an ellipsis) or is followed by a space, I want to leave it alone.</p>
