Test protected flag retained during redefinition.

- Add expand and toRdf tests to check protection flag is retained when a
  term is redefined the same as a protected term, and then redefined as
  something else, triggering a failure.
- See 4.1.11 https://www.w3.org/TR/json-ld11/#protected-term-definitions
  about similar overrides that don't change semantics of the protected
  term.
- See 4.2.2.27.2 https://www.w3.org/TR/json-ld-api/#algorithm-0 about
  retaining the value of protected flag.

tests/expand-manifest.jsonld

@@ -2843,6 +2843,14 @@
       "option": {"specVersion": "json-ld-1.1"},
       "input": "expand/pr41-in.jsonld",
       "expect": "expand/pr41-out.jsonld"
+    }, {
+      "@id": "#tpr42",
+      "@type": ["jld:NegativeEvaluationTest", "jld:ExpandTest"],
+      "name": "Fail if protected flag not retained during redefinition",
+      "purpose": "Check protected redefinition retains protected flag.",
+      "option": {"specVersion": "json-ld-1.1"},
+      "input": "expand/pr42-in.jsonld",
+      "expectErrorCode": "protected term redefinition"
     }, {
       "@id": "#tso01",
       "@type": ["jld:NegativeEvaluationTest", "jld:ExpandTest"],

tests/expand/pr42-in.jsonld

@@ -0,0 +1,15 @@
+{
+  "@context": [
+    {
+      "@protected": true,
+      "protected": "ex:protected"
+    },
+    {
+      "protected": "ex:protected"
+    },
+    {
+      "protected": "ex:unprotected"
+    }
+  ],
+  "protected": "fail / protection not retained during redefinition"
+}

tests/toRdf-manifest.jsonld

@@ -3372,6 +3372,14 @@
       "option": {"specVersion": "json-ld-1.1"},
       "input": "toRdf/pr41-in.jsonld",
       "expect": "toRdf/pr41-out.nq"
+    }, {
+      "@id": "#tpr42",
+      "@type": ["jld:NegativeEvaluationTest", "jld:ToRDFTest"],
+      "name": "Fail if protected flag not retained during redefinition",
+      "purpose": "Check protected redefinition retains protected flag.",
+      "option": {"specVersion": "json-ld-1.1"},
+      "input": "toRdf/pr42-in.jsonld",
+      "expectErrorCode": "protected term redefinition"
     }, {
       "@id": "#trt01",
       "@type": ["jld:PositiveEvaluationTest", "jld:ToRDFTest"],

tests/toRdf/pr42-in.jsonld

@@ -0,0 +1,15 @@
+{
+  "@context": [
+    {
+      "@protected": true,
+      "protected": "ex:protected"
+    },
+    {
+      "protected": "ex:protected"
+    },
+    {
+      "protected": "ex:unprotected"
+    }
+  ],
+  "protected": "fail / protection not retained during redefinition"
+}