Rename the internal "EP_Constant" bitmask to a less misleading "EP_ConstFunc".

FossilOrigin-Name: 4ef7ceced2b0000d21f7f8014384c04a0e4661d3
diff --git a/src/expr.c b/src/expr.c
index 25bd958..2f0fe4a 100644
--- a/src/expr.c
+++ b/src/expr.c
@@ -1249,7 +1249,7 @@
     ** and either pWalker->eCode==4 or 5 or the function has the
     ** SQLITE_FUNC_CONST flag. */
     case TK_FUNCTION:
-      if( pWalker->eCode>=4 || ExprHasProperty(pExpr,EP_Constant) ){
+      if( pWalker->eCode>=4 || ExprHasProperty(pExpr,EP_ConstFunc) ){
         return WRC_Continue;
       }else{
         pWalker->eCode = 0;