travis: add bitcoind test without txindex

.travis.yml

@@ -52,11 +52,16 @@ jobs:
       script:
         - make itest
 
-    - name: Bitcoind Integration
+    - name: Bitcoind Integration (txindex enabled)
       script:
         - bash ./scripts/install_bitcoind.sh
         - make itest backend=bitcoind
 
+    - name: Bitcoind Integration (txindex disabled)
+      script:
+        - bash ./scripts/install_bitcoind.sh
+        - make itest backend="bitcoind notxindex"
+
     - name: Neutrino Integration
       script:
         - make itest backend=neutrino