updated VERSION for 2.3.11
bumped Symfony version to 2.3.12
fixed Kernel::stripComments() normalizing new-lines

This makes normalizing new-lines less error-prone
when a string contains multiple new line-lines
Merge branch '2.3' into 2.4

* 2.3:
  changed some PHPUnit assertions to more specific ones
  fixed Kernel::stripComments() normalizing new-lines
  added a BC comment
  Update FileLoader to fix issue #10339