Description:
------------
There is no documented array concatenation function. This is a very common function, e.g. Javascript and Ruby have the `concat` function, Python has `+` and Haskell has `++`. 

The `array_merge` function (http://php.net/manual/en/function.array-merge.php) is what has be used if you want to concatenate arrays. However it is not mentioned in the documentation (not even in the comments) of that method that that is what should be used.

I propose that `array_concat` be created as an alias of `array_merge`. The concatenation of an associative array is also consistent with trying to merge the hash maps. For example this Stack Overflow question on [concatenating two dictionaries](http://stackoverflow.com/questions/1781571/how-to-concatenate-two-dictionaries-to-create-a-new-one-in-python#1784128) is marked as a duplicate of the function 'How to merge two Python dictionaries'. That is, it is consistent that hash map concatenation is the same as hash map merging.

So I believe that `array_concat` is a perfect alias for `array_merge` in terms of numeric arrays and a valid (albeit unnecessary) alias for associative arrays.

This will help almost all developers coming to PHP from other dynamic languages. 

Test script:
---------------
<?php
var_dump(array_concat(array('London'), array('Calling')));
?>



Expected result:
----------------
array(2) {
  [0]=>
  string(6) "London"
  [1]=>
  string(7) "Calling"
}