title: Python fromtimestamp OSError
body: <p>For some reason when constructing datetimes using fromtimestamp, I get a "OSError [Errno22] Invalid Argument" when I use negative times less than -43200 (-12hrs).
  I am on Win7 64-bit and python 3.5.1. Here's code that produces the error.</p>
  
  <pre><code>&gt;&gt;&gt; import datetime
  &gt;&gt;&gt; import pytz
  &gt;&gt;&gt; datetime.datetime.fromtimestamp(-43200, pytz.utc)
  datetime.datetime(1969, 12, 31, 12, 0, tzinfo=&lt;UTC&gt;)
  &gt;&gt;&gt; datetime.datetime.fromtimestamp(-43201, pytz.utc)
  Traceback (most recent call last):
    File "&lt;stdin&gt;", line 1, in &lt;module&gt;
  OSError: [Errno 22] Invalid argument
  </code></pre>
  
  <p>The sample uses pytz to simplify timezone information, but the error also occurs without it.</p>