function: Logical_xor Purpose: IDL has logical_and, and logical_or, but not logical_xor This routine add this capability $LastChangedBy: pcruce $ $LastChangedDate: 2009-06-12 11:33:39 -0700 (Fri, 12 Jun 2009) $ $LastChangedRevision: 6178 $ $URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/spdsoft/trunk/general/misc/SSW/logical_xor.pro $