Updated mediawiki/extensions
Project: mediawiki/extensions/ExtensionDistributor  734c29286b4b5e32c0ebc0c0f1d598c7302d5bc3
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Rename $wgExtDistBranches to $wgExtDistSnapshotRefs

It's more descriptive for what it really does now, and allows
me to configure it in CommonSettings before deploying.

Change-Id: Ide2281b70012374986d654b0cf68b4dd6bdce020