[Config] Fix missing argument

If YamlUserLoader corresponds to the definition above (which extends
FileLocator), then it should receive a FileLocatorInterface for the
first argument of its constructor.
fixed some file extensions
Fixing index typo
fixed typo (configured to do sth, not 'does sth')
Update book/propel.rst
Fix path of an example file
Merge pull request #1623 from MattKetmo/fix-config

[Config] Fix missing argument
Merge pull request #1625 from bamarni/file-extensions

fixed some file extensions
Added links to the DOMCrawler and CSS Selector components from testing page
Tidied up a bit of grammar and added a link to the EventDispatcher docs in the before/after filters article
Merge pull request #1631 from richardmiller/adding_links_to_relevant_components

Added links to the DOMCrawler and CSS Selector components from testing page
Re-adding article to cookbook map that had gotten lost
Fixed indentation.
Added change that brought me in doubt while doing this in my code
[#1632] Adding even more clarification for the importance of making a response public
Update components/dependency_injection/compilation.rst

fixed variable names in sample
fixed typos
made use of static:: instead of (and inherit from parent's tearDown method)
Added kernel.event_subscriber to tags list
Fixing 2 unrelated syntax issues