title: Using strptime to parse timestamp relative to the local time
body: <p>I am trying to do some date calculation relative to the current local time. 
  For example:</p>
  
  <pre><code>use feature qw(say);
  use strict;
  use warnings;
  
  use Time::Piece;
  
  my $fmt = '%Y-%m-%d_%H:%M:%S';
  my $timestamp = "2015-04-12_11:07:27";
  
  # This gives incorrect $t1 relative to localtime
  my $t1 = Time::Piece-&gt;strptime( $timestamp, $fmt );
  my $t2 = localtime;
  
  say "Local time: " . localtime;
  say "Local time epoch: " . time;
  
  say $t1-&gt;epoch();
  say $t2-&gt;epoch();
  
  my $timestamp1 = $t1-&gt;strftime( $fmt );
  my $timestamp2 = $t2-&gt;strftime( $fmt );
  
  say $timestamp1;
  say $timestamp2;
  
  my $delta = $t2 - $t1;
  
  say $delta;
  </code></pre>
  
  <p>A sample output:</p>
  
  <pre><code>Local time: Sun Apr 12 12:21:49 2015
  Local time epoch: 1428834109
  1428836847
  1428834109
  2015-04-12_11:07:27
  2015-04-12_12:21:49
  -2738
  </code></pre>
  
  <p>Which clearly gives the a wrong time difference of -2738. ( It should be a positive number)</p>