Add missing const declarations.

src/varscan.c

@@ -821,7 +821,7 @@ int varDefGrid(int vlistID, grid_t grid, int mode)
 }
 
 
-int zaxisCompare(int zaxisID, int zaxistype, int nlevels, int lbounds, double *levels, char *longname, char *units, int ltype1)
+int zaxisCompare(int zaxisID, int zaxistype, int nlevels, int lbounds, const double *levels, char *longname, char *units, int ltype1)
 {
   int differ = 1;
   int levelID;

src/varscan.h

@@ -38,7 +38,7 @@ void varDefOptGribInt(int varID, long lval, const char *keyword);
 void varDefOptGribDbl(int varID, double dval, const char *keyword);
 int varOptGribNentries(int varID);
 
-int  zaxisCompare(int zaxisID, int zaxistype, int nlevels, int lbounds, double *levels, char *longname, char *units, int ltype);
+int  zaxisCompare(int zaxisID, int zaxistype, int nlevels, int lbounds, const double *levels, char *longname, char *units, int ltype);
 
 #endif
 /*

src/vlist.c

@@ -444,8 +444,8 @@ void vlistClearFlag(int vlistID)
 }
 
 static
-int vlist_generate_zaxis(int vlistID, int zaxistype, int nlevels, double *levels,
-                         double *lbounds, double *ubounds, int vctsize, const double *vct)
+int vlist_generate_zaxis(int vlistID, int zaxistype, int nlevels, const double *levels,
+                         const double *lbounds, const double *ubounds, int vctsize, const double *vct)
 {
   int zaxisID = CDI_UNDEFID;
   int zaxisglobdefined = 0;