Linux: warn when a mounted volume depends on the requester's session

A volume file opened with the credentials of the requesting user is
served by a file system that belongs to that user's session. Ejecting
the share or logging out while the volume is mounted can lose data, and
GVfs does not refuse to eject a share whose file is in use. Warn after
each such mount that the share must stay mounted and the session active
until the volume is unmounted. Append the English message to all
language files as a fallback.

The indicator reaches the UI with the mount result, through a new
MountVolumeRequestV2/ResponseV2 pair: a service that predates it rejects
the new request before mounting, and legacy requests keep their legacy
response, so that an older UI still works with a newer service. The
control file format is unchanged.

src/Core/Unix/CoreService.cpp

@@ -1337,9 +1337,13 @@ namespace VeraCrypt
 					MountVolumeRequest *mountRequest = dynamic_cast <MountVolumeRequest*> (request.get());
 					if (mountRequest)
 					{
-						MountVolumeResponse (
-							Core->MountVolume (*mountRequest->Options)
-						).Serialize (outputStream);
+						shared_ptr <VolumeInfo> mountedVolume = Core->MountVolume (*mountRequest->Options);
+#ifdef TC_LINUX
+						if (dynamic_cast <MountVolumeRequestV2*> (mountRequest))
+							MountVolumeResponseV2 (mountedVolume).Serialize (outputStream);
+						else
+#endif
+							MountVolumeResponse (mountedVolume).Serialize (outputStream);
 
 						continue;
 					}
@@ -1454,8 +1458,13 @@ namespace VeraCrypt
 
 	shared_ptr <VolumeInfo> CoreService::RequestMountVolume (MountOptions &options)
 	{
+#ifdef TC_LINUX
+		MountVolumeRequestV2 request (&options);
+		return SendRequest <MountVolumeResponseV2> (request)->MountedVolumeInfo;
+#else
 		MountVolumeRequest request (&options);
 		return SendRequest <MountVolumeResponse> (request)->MountedVolumeInfo;
+#endif
 	}
 
 	void CoreService::RequestSetFileOwner (const FilesystemPath &path, const UserId &owner)