Changed calculation of scattering angle in elastic scattering to use dot product.
Changed calculation of scattering angle in elastic scattering to use dot product.

shikhar413/openmc,wbinventor/openmc,liangjg/openmc,walshjon/openmc,kellyrowland/openmc,mit-crpg/openmc,wbinventor/openmc,shikhar413/openmc,johnnyliu27/openmc,liangjg/openmc,shenqicang/openmc,walshjon/openmc,shenqicang/openmc,paulromano/openmc,samuelshaner/openmc,bhermanmit/openmc,lilulu/openmc,smharper/openmc,samuelshaner/openmc,keadyk/openmc_mg_prepush,keadyk/openmc_mg_prepush,smharper/openmc,bhermanmit/cdash,mjlong/openmc,amandalund/openmc,johnnyliu27/openmc,liangjg/openmc,kellyrowland/openmc,mit-crpg/openmc,lilulu/openmc,johnnyliu27/openmc,shikhar413/openmc,mit-crpg/openmc,johnnyliu27/openmc,walshjon/openmc,lilulu/openmc,paulromano/openmc,amandalund/openmc,wbinventor/openmc,sxds/opemmc,liangjg/openmc,sxds/opemmc,nhorelik/openmc,amandalund/openmc,shikhar413/openmc,bhermanmit/openmc,smharper/openmc,amandalund/openmc,smharper/openmc,paulromano/openmc,mjlong/openmc,nhorelik/openmc,keadyk/openmc_mg_prepush,wbinventor/openmc,paulromano/openmc,walshjon/openmc,mit-crpg/openmc,samuelshaner/openmc,samuelshaner/openmc