Fix copy(into:) overwrite mode

Seems like Linux Foundation has a bug

I checked, seems fixed in Swift 5. But added a swift version check se we can verify and if not report the bug.

Tests/PathTests/PathTests.swift

@@ -138,4 +138,15 @@ class PathTests: XCTestCase {
         XCTAssertEqual(Path.root/"a/foo"/"../../bar", Path.root/"bar")
         XCTAssertEqual(Path.root/"a/foo"/"../../../bar", Path.root/"bar")
     }
+
+    func testCopyInto() throws {
+        try Path.mktemp { root in
+            let bar = try root.join("bar").touch()
+            try Path.mktemp { root in
+                try root.join("bar").touch()
+                XCTAssertThrowsError(try bar.copy(into: root))
+                try bar.copy(into: root, overwrite: true)
+            }
+        }
+    }
 }

Tests/PathTests/XCTestManifests.swift

@@ -5,6 +5,7 @@ extension PathTests {
         ("testBasename", testBasename),
         ("testCodable", testCodable),
         ("testConcatenation", testConcatenation),
+        ("testCopyInto", testCopyInto),
         ("testEnumeration", testEnumeration),
         ("testEnumerationSkippingHiddenFiles", testEnumerationSkippingHiddenFiles),
         ("testExists", testExists),