Build and run compiler tests in appveyor

Author: fuine

appveyor.yml

@@ -52,3 +52,5 @@ build: false
 test_script:
   - cargo build --verbose --target %TARGET%
   - cargo test --target %TARGET%
+  - if "%CHANNEL%" == "nightly" cargo build --verbose --target %TARGET% --features "compiletest"
+  - if "%CHANNEL%" == "nightly" cargo test --target %TARGET% --features "compiletest"