title: merge two arrays, while maintaining the numeric keys
body: <p>im trying to merge two arrays together.  both have numeric keys and are unique.  when i use array_merge, it re-indexes starting at 0.</p>
  
  <p>so lets say i have </p>
  
  <pre><code>[2] = abc
  [5] = cde
  </code></pre>
  
  <p>and i have</p>
  
  <pre><code>[32] = fge
  [13] = def
  </code></pre>
  
  <p>i want to merge these two together maintaining the unique keys.</p>
  
  <p>below is the explaination on the current merge behavior.. any way around this?</p>
  
  <p>"If all of the arrays contain only numeric keys, the resulting array is given incrementing keys starting from zero."</p>