Don't ignore files with use function

[weirdan]

Previously ClassFileLocator would enter a "function context" when it encountered T_FUNCTION token, causing it to ignore subsequent classes (thinking they are defined in a function), ultimately leading to the file being ignored because ClassFileLocator thought there's no (named) classes defined in the file.

Now it will additionally check that the T_FUNCTION token is not preceded by T_USE, fixing the bug.

Steps to reproduce:

• Create a file, containing a class, and import a function in that class with use function (see ContainsUseFunction.php in the test asset folder).
• Create a ClassFileLocator for a folder containing that file
• Iterate over the locator

Expected

The file should be found, and contain the class

Actual

The file is ignored

Checklist

• Are you fixing a bug?
  • Detail how the bug is invoked currently.
  • Detail the original, incorrect behavior.
  • Detail the new, expected behavior.
  • Base your feature on the master branch, and submit against that branch.
  • Add a regression test that demonstrates the bug, and proves the fix.
  • Add a CHANGELOG.md entry for the fix.

[weierophinney]

Thanks, @weirdan!