Fix Travis, Windows core tests

- Update travis config to fix xvfb problem
- Update tests/core/tests submodule for Windows
- Specify configuration when running ctest

Author: cxw42

.appveyor.yml

@@ -94,7 +94,7 @@ build_script:
 
 test_script:
   # Run the core tests
-  - ctest . --output-on-failure
+  - ctest . --output-on-failure -C Debug
 
   # CTestCustom specifies skipping UTF-8 tests on Windows.
   - cmd: echo "Reminder - did not try UTF-8"

.gitmodules

@@ -3,4 +3,5 @@
 	url = https://github.com/editorconfig/editorconfig-plugin-tests.git
 [submodule "core_tests"]
 	path = tests/core/tests
-	url = https://github.com/editorconfig/editorconfig-core-test.git
+	url = https://github.com/cxw42/editorconfig-core-test.git
+	branch = cxwtest

.travis.yml

@@ -1,3 +1,6 @@
+# Make sure xvfb works - https://docs.travis-ci.com/user/gui-and-headless-browsers/#using-xvfb-directly
+dist: trusty
+
 matrix:
   include:
     - name: "plugin"

tests/core/tests

@@ -14,5 +14,7 @@ else                                        # test core
     mkdir build
     cd build
     cmake ..
-    ctest . --output-on-failure
+    ctest . --output-on-failure -VV -C Debug
+    	# -C Debug: for Visual Studio builds, you have to specify
+	# a configuration.
 fi