ENH: provide argList::envGlobalPath() static method

- this is identical to either of these solutions:

     * getEnv("FOAM_CASE")
     * stringOps::expand("<case>")

  but with a closer resemblance to argList or Time globalPath(),
  which makes the intent clearer.
  Avoids using raw strings in the caller, which improves compile-time checks.

  Used in situations where a class has no derivation path or other
  access to a time registry or command args.

src/functionObjects/utilities/systemCall/systemCall.C

@@ -114,9 +114,17 @@ bool Foam::functionObjects::systemCall::read(const dictionary& dict)
     if (executeCalls_.empty() && endCalls_.empty() && writeCalls_.empty())
     {
         WarningInFunction
-            << "no executeCalls, endCalls or writeCalls defined."
+            << "No executeCalls, endCalls or writeCalls defined."
             << endl;
     }
+    else if (isAdministrator())
+    {
+        FatalErrorInFunction
+            << "System calls should not be executed by someone"
+            << " with administrator rights for security reasons." << nl
+            << nl << endl
+            << exit(FatalError);
+    }
     else if (!dynamicCode::allowSystemOperations)
     {
         FatalErrorInFunction