[Config] Adding the previous exception message into the FileLoaderLoadException so it's more easily seen

In the framework if you, for example, make a syntax error in YAML, then the true, clear message (e.g. Unable to parse at line 5 (near "framework") is nested, and harder to visually see. This includes that message in the main exception so that users can debug more easily.

Before: Cannot import resource "/path/to/app/config/config.yml" from "/path/to/app/config/config_dev.yml".

After: Cannot import resource "/path/to/app/config/config.yml" from "/path/to/app/config/config_dev.yml". (Unable to parse at line 5 (near "framework").)
Merge branch '2.3'

* 2.3: (37 commits)
  [Console] renamed ConsoleForExceptionEvent into ConsoleExceptionEvent
  Fix several instances of doubled words
  [Security] Fixed the check if an interface exists.
  Added missing slovak translations
  [FrameworkBundle] removed HttpFoundation classes from HttpKernel cache
  [Finder] Fix iteration fails with non-rewindable streams
  [Finder] Fix unexpected duplicate sub path related AppendIterator issue
  [Security] Added tests for the DefaultLogoutSuccessHandler.
  [Security] Added tests for the DefaultAuthenticationSuccessHandler.
  [ClassLoader] tiny refactoring
  [Security] Added tests for the DefaultAuthenticationFailureHandler.
  [Security] Added tests for the remember me ReponseListener.
  [Security] Added tests for the SessionAuthenticationStrategy.
  [Security] Added tests for the AccessMap.
  [FrameworkBundle] removed deprecated method from cache:clear command
  [WebProfiler] remove deprecated verbose option
  fix logger in regards to DebugLoggerInterface
  [Form] [2.3] removed old option
  Added type of return value in VoterInterface.
  [Console] Add namespace support back in to list command
  ...