Enforce multi-line String Concat Spacing

[ofbeaton]

This should be the only valid case:

function myfunc()
{
   $myString = 'This is a really long string.'
      .' It needs to be broken over many lines to observe PSR-2 120-char limit';
}

This is already invalid:

function myfunc()
{
   $myString = 'This is a really long string.'
.' It needs to be broken over many lines to observe PSR-2 120-char limit';
}

The following 2 are currently valid but should not be:

function myfunc()
{
   $myString = 'This is a really long string.'
   .' It needs to be broken over many lines to observe PSR-2 120-char limit';
}

function myfunc()
{
   $myString = 'This is a really long string.'
         .' It needs to be broken over many lines to observe PSR-2 120-char limit';
}

We would need to make our own concat sniff that enforced this.