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