How to implement check all/uncheck all in dirPagination?

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Hi, thanks for contributing!

This project is maintained in my spare time, so in order to help me address your issue as quickly as
possible, please provide as much of the following information as you can:

- Title: Please indicate the module in question, e.g. "dirPagination: X is broken when Y"
- If reporting on dirPagination, please include the version you are using (can be found in the package.json / bower.json file)
- If you are able to reproduce your issue on Plunker, this will vastly increase the chances of a rapid response from me.

-- Michael

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(Delete the above. Fill in the rest as applicable)

**Description of issue**:

**Steps to reproduce**:

**Expected result**:

**Actual result**:

**Demo**: (for dirPagination, fork and modify this Plunk: http://plnkr.co/edit/b37IdFFJUokaeSummETX?p=preview)

Any relevant code:
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Start by locating the dirPagination implementation and reviewing its existing selection behavior. The issue provides no reproduction, expected result, demo, or relevant code, so clarify the intended check-all and uncheck-all behavior before identifying the changes and verification needed.

Written by the indexing model from the issue text.