Present case of class and interface names.

Summary: Currently, class and interface names are converted to lowercase when comparing minimum and maximum versions. This is necessary in order to compare with the data from `php_compat_info.json` but causes the lint message to be slightly misleading.

Test Plan:
Linted a test file.

**Before**
```
   Error  (XHP31) Use Of PHP 5.3 Features
    This codebase targets PHP 5.2.3, but `iterator` was not introduced until
    PHP 5.3.0.

               1 <?php
               2
    >>>        3 final class FooBar implements Iterator {}
```

**After**
```
   Error  (XHP31) Use Of PHP 5.3 Features
    This codebase targets PHP 5.2.3, but `Iterator` was not introduced until
    PHP 5.3.0.

               1 <?php
               2
    >>>        3 final class FooBar implements Iterator {}
```

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9471