Switch Windows CI builds from windows-gnu to windows-msvc.

The Travis default of windows-gnu suffers from rust-lang/rust#47048, I
think. I don't see an easy way to address this right now, but switching
our Windows builds to windows-msvc will avoid this and is more realistic
target anyway.

.travis.yml

@@ -13,11 +13,15 @@ env:
     - RELEASE=
     - RELEASE=--release
 
+install:
+  - if [ "$TRAVIS_OS_NAME" = "windows" ]; then rustup target add x86_64-pc-windows-msvc; fi
+
 script:
   # We cannot run `cargo test` with the mp4parse_fallible feature enabled
   # (see comment where the feature is defined in mp4parse_capi/Cargo.toml),
   # but we can at least check for changes behind features that would break the
   # build.
   - cargo check --all --verbose $RELEASE --tests --all-features
-  - cargo test --all --verbose $RELEASE
+  - if [ "$TRAVIS_OS_NAME" = "windows" ]; then export TARGET=--target=x86_64-pc-windows-msvc; fi
+  - cargo test --all --verbose $RELEASE $TARGET -- --nocapture
   - cargo doc --package mp4parse_capi

test_ffi/src/main.rs

@@ -27,11 +27,16 @@ fn ffi_test() {
     extern { fn test_main(test_path: *const c_char) -> c_void; }
 
     let path = {
-        let argv0 = std::env::args().next().unwrap();
-        let mut base = std::path::PathBuf::from(argv0);
-        base.pop();
-        base.push("../../../mp4parse/tests/minimal.mp4");
-        let path = base.canonicalize().unwrap();
+        let base = std::env::var("CARGO_MANIFEST_DIR").unwrap();
+        eprintln!("debug base={:?}", base);
+        let mut path = std::path::PathBuf::from(base);
+        eprintln!("debug path={:?}", path);
+        path.pop();
+        eprintln!("debug path={:?}", path);
+        path.push("mp4parse/tests/minimal.mp4");
+        eprintln!("debug path={:?}", path);
+        let path = path.canonicalize().unwrap();
+        eprintln!("debug path={:?}", path);
 
         #[cfg(unix)]
         {