Remove leading slashes in use clauses.

- Addresses FriendsOfPHP/PHP-CS-Fixer#705
- Renaming getNamespaceUseIndexes -> getImportUseIndexes
feature #706 Remove lead slash (dericofilho)

This PR was merged into the 1.2-dev branch.

Discussion
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Remove lead slash

Addresses FriendsOfPHP/PHP-CS-Fixer#705

Commits
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fed06f4 Remove leading slashes in use clauses.