Make allow_backtprop also a particle element in McXtrace

Author: willend

mccode/src/cogen.c.in

@@ -1609,9 +1609,9 @@ void def_trace_section(struct instr_def *instr)
           "x", "y", "z", "vx", "vy", "vz",
           "t", "sx", "sy", "sz", "p", "mcgravitation", "mcMagnet", "allow_backprop", "_mctmp_a", "_mctmp_b", "_mctmp_c"
   #elif MCCODE_PROJECT == 2   /* xray */
-  #define NUM_STATE_PARS 15
+  #define NUM_STATE_PARS 16
           "x", "y", "z", "kx", "ky", "kz",
-          "phi", "t", "Ex", "Ey","Ez", "p", "_mctmp_a", "_mctmp_b", "_mctmp_c"
+          "phi", "t", "Ex", "Ey","Ez", "p", "allow_backprop", "_mctmp_a", "_mctmp_b", "_mctmp_c"
   #endif
   };