Change the version number to 3.6.19.  Fix a couple of incorrect testcase()
macros associated with the new IS and IS NOT operators in expr.c.

FossilOrigin-Name: e3b73394bf9c0391e997079b160eace3589415ab
diff --git a/src/expr.c b/src/expr.c
index 998bf41..06db149 100644
--- a/src/expr.c
+++ b/src/expr.c
@@ -3195,8 +3195,8 @@
     }
     case TK_IS:
     case TK_ISNOT: {
-      testcase( op==TK_IS );
-      testcase( op==TK_ISNOT );
+      testcase( pExpr->op==TK_IS );
+      testcase( pExpr->op==TK_ISNOT );
       codeCompareOperands(pParse, pExpr->pLeft, &r1, &regFree1,
                                   pExpr->pRight, &r2, &regFree2);
       op = (pExpr->op==TK_IS) ? TK_NE : TK_EQ;