Makes custom-made sniffs cross-version compatible

1. fixing several sniffs to be compatible with PHPCS 1.x and 2.x at same time:
- "ValidFunctionName"
- "InlineComment"
- "FunctionComment"
2. adding wrapper for DocCommentSniff, created in PHPCS 2.x, to prevent error about missing sniff on PHPCS 1.x
3. consider PHPCS 2.x tests failure as build failure, because now all tests pass there