Dedupe affiliations

[justinlittman]

For example:

<author role="corresp">
                            <persName>
                                <forename type="first">Boris</forename>
                                <forename type="middle">B</forename>
                                <surname>Shin</surname>
                            </persName>
                            <affiliation key="aff0">
                                <orgName type="department">Stanford Center for Innovations in Learning</orgName>
                                <orgName type="institution">Stanford University</orgName>
                                <address>
                                    <addrLine>450 Serra Mall, Building 160</addrLine>
                                    <postCode>94305-2055</postCode>
                                    <settlement>Stanford</settlement>
                                    <region>CA</region>
                                </address>
                            </affiliation>
                            <affiliation key="aff3">
                                <orgName type="department">Stanford Center for Innovations in Learning</orgName>
                                <orgName type="institution">Stanford University</orgName>
                                <address>
                                    <addrLine>450 Serra Mall Building 160</addrLine>
                                    <postCode>94305-2055</postCode>
                                    <settlement>Stanford</settlement>
                                    <region>CA</region>
                                </address>
                            </affiliation>
                            <affiliation key="aff0">
                                <orgName type="department">Stanford Center for Innovations in Learning</orgName>
                                <orgName type="institution">Stanford University</orgName>
                                <address>
                                    <addrLine>450 Serra Mall, Building 160</addrLine>
                                    <postCode>94305-2055</postCode>
                                    <settlement>Stanford</settlement>
                                    <region>CA</region>
                                </address>
                            </affiliation>
                            <affiliation key="aff3">
                                <orgName type="department">Stanford Center for Innovations in Learning</orgName>
                                <orgName type="institution">Stanford University</orgName>
                                <address>
                                    <addrLine>450 Serra Mall Building 160</addrLine>
                                    <postCode>94305-2055</postCode>
                                    <settlement>Stanford</settlement>
                                    <region>CA</region>
                                </address>
                            </affiliation>
                        </author>