[ticket/12268] Extension finder should not crawl through .git/ of extensions

This new filter ignores .svn and .git directories.
When searching for php classes and template files of extensions
we don't need to look inside these directories.

PHPBB3-12268
[ticket/12268] Use FilesystemIterator::SKIP_DOTS

PHPBB3-12268
[ticket/12268] Do not search in folders starting with a dot

PHPBB3-12268
[ticket/12268] Move class out of extension namespace and rename it

PHPBB3-12268
[ticket/12268] Rename class file to recursive_dot_prefix_filter_iterator.php

PHPBB3-12268
[ticket/12268] Do not use substr but just compare the character

PHPBB3-12268
Merge remote-tracking branch 'nickvergessen/ticket/12268' into develop-ascraeus

# By Joas Schilling
# Via Joas Schilling
* nickvergessen/ticket/12268:
  [ticket/12268] Do not use substr but just compare the character
  [ticket/12268] Rename class file to recursive_dot_prefix_filter_iterator.php
  [ticket/12268] Move class out of extension namespace and rename it
  [ticket/12268] Do not search in folders starting with a dot
  [ticket/12268] Use FilesystemIterator::SKIP_DOTS
  [ticket/12268] Extension finder should not crawl through .git/ of extensions