Fix build script bug

Determine if current DirectoryIterator item is a symbolic link

1) CacheTest::testDataMemcachedCache

PHP Notice: Undefined index: SCRIPT_NAME in /home/travis/.phpenv/versions/5.5.0/share/pyrus/.pear/php/PHPUnit/Util/Filter.php on line 69

Notice: Undefined index: SCRIPT_NAME in /home/travis/.phpenv/versions/5.5.0/share/pyrus/.pear/php/PHPUnit/Util/Filter.php on line 69

Failed asserting that false is true