The "ConcatenationSpacingSniff" should validate extra spaces

[aik099]

Right now "ConcatenationSpacingSniff" sniff validates, that at least one space is used to concatenate parts of a string. We should change it to be exactly one space.

In case if previous/next string ends up on another line we shouldn't validate other half:

// check both spaces
$s1 = 'a' . 'b';

// only check space before dot
$s2 = 'a' .
'b';

// only check space after dot
$s3 = 'a'
. 'b';

File: https://github.com/aik099/CodingStandard/blob/master/CodingStandard/Sniffs/Strings/ConcatenationSpacingSniff.php

[aik099]

Currently new line symbols and indentation tabs appear as spaces in comparison and all seems valid.