Clarify Coding Standards (DIRECTORY_SEPARATOR)

[sghoweri]

@EvanLovely specifically, which of these is "correct" here? Do we actually need / use / require DIRECTORY_SEPARATOR still? Is there a better way to handle this sort of thing?

// PatternInfoRule.php
$filePath = Config::getOption("patternSourceDir")."/".$pathName;`

// PsuedoPatternRule.php
$filePath = Config::getOption("patternSourceDir").DIRECTORY_SEPARATOR.$pathName;`

// DocumentationRule.php
$patternSourceDir = Config::getOption("patternSourceDir");
$filePath = $patternSourceDir.DIRECTORY_SEPARATOR.$pathName;