bpo-33764: Appveyor fixes (GH-7364)

* Prevent spurious message if taking a shortcut
* Fix YAML style
* Disable largefile tests

.github/appveyor.yml

@@ -20,9 +20,10 @@ before_build:
         If (!$changes) {
           echo 'Only docs were updated, stopping build process.'
           Exit-AppveyorBuild
+        } else {
+          echo 'Doing full build due to non-doc changes in these files:'
+          echo $changes
         }
-        echo 'Doing full build due to non-doc changes in these files:'
-        echo $changes
       }
 
 
@@ -30,8 +31,8 @@ build_script:
   - cmd: PCbuild\build.bat -e
   - cmd: PCbuild\win32\python.exe -m test.pythoninfo
 test_script:
-  - cmd: PCbuild\rt.bat -q -uall -u-cpu -rwW --slowest --timeout=1200 --fail-env-changed -j0
+  - cmd: PCbuild\rt.bat -q -uall -u-cpu -u-largefile -rwW --slowest --timeout=1200 --fail-env-changed -j0
 environment:
   HOST_PYTHON: C:\Python36\python.exe
 image:
-- Visual Studio 2017
+  - Visual Studio 2017