Updated the code based on the https://github.com/JetBrains/intellij-community/blob/135/platform/lang-impl/src/com/intellij/find/actions/ShowUsagesAction.java file

Signed-off-by: Carlos Sobrinho <carlos@sobrinho.pt>
Merge pull request #10 from csobrinho/fix-issue-8

Updated the code based on Intellij 13.1