similar change for using C_DOUBLE vice real(8)
similar change for using C_DOUBLE vice real(8)

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