Allow SettingsFile.source to have multiple source distributions
Allow SettingsFile.source to have multiple source distributions

amandalund/openmc,johnnyliu27/openmc,bhermanmit/openmc,walshjon/openmc,walshjon/openmc,kellyrowland/openmc,walshjon/openmc,wbinventor/openmc,smharper/openmc,wbinventor/openmc,paulromano/openmc,amandalund/openmc,paulromano/openmc,shikhar413/openmc,samuelshaner/openmc,paulromano/openmc,smharper/openmc,bhermanmit/openmc,smharper/openmc,liangjg/openmc,johnnyliu27/openmc,shikhar413/openmc,walshjon/openmc,samuelshaner/openmc,mit-crpg/openmc,mit-crpg/openmc,smharper/openmc,wbinventor/openmc,amandalund/openmc,paulromano/openmc,johnnyliu27/openmc,shikhar413/openmc,samuelshaner/openmc,wbinventor/openmc,shikhar413/openmc,mit-crpg/openmc,liangjg/openmc,amandalund/openmc,kellyrowland/openmc,johnnyliu27/openmc,liangjg/openmc,liangjg/openmc,samuelshaner/openmc,mit-crpg/openmc