title: AM/PM string is not properly recognized by strptime
body: <p>I have encountered something unexpected while working with the function strptime(). The format of the date I have consists of "1/22/2013 11:00:00 P.M" . The format I am using for this is "%m/%d/%Y %I:%M:%S %p".</p>
  
  <p>The code is as follows.</p>
  
  <pre><code>strptime("1/22/2013 11:00:00 p.m",format="%m/%d/%Y %I:%M:%S %p")
  [1] NA
  </code></pre>
  
  <p>but if I use </p>
  
  <pre><code>strptime("1/22/2013 11:00:00 pm",format="%m/%d/%Y %I:%M:%S %p")
  [1] "2013-01-22 23:00:00"
  </code></pre>
  
  <p>I get the appropriate result.</p>
  
  <p>So does this feature lack in strptime to detect p.m and its variations such as p.m. etc in place of PM or pm. Is this a bug in R ?</p>
  
  <p>The version of R I am using R.14.2 on windows 7 32-bit</p>