svn merge -r134817:136516 svn+ssh://svn.lindenlab.com/svn/linden/branches/avatar-pipeline/avatar-pipeline-multiattachments-3 into svn+ssh://svn.lindenlab.com/svn/linden/branches/viewer/viewer-2.0.0-3

For DEV-32867 : Avatar Pipeline Project - Multi-Attachments

This is a viewer-side-only, infrastructure-only merge for multi-attachments.  This should not lead to any new functionality; it simply provides backwards compatibility for when multi-attachments are enabled in viewer2.1, so that viewer2.0 users can see viewer2.1 avatars correctly.

Reviewed by: Vir.