Stage 6 of clang compiler warning patches.

[ethoms]

Stage 6:

Missing method implementations:
(i) 'changeParticipationStatus' is a missing protocol method in SoObjects/Appointments/SOGoCalendarComponent.m. So I added a dummy one that just returns nil.
(ii) 'appendCollectedSources' is a missing method in 'SOGoParentFolder'. It does exist in a class called 'SOGoContactFolders' which is a subclass (child) of 'SOGoParentFolder'. So I copied that method to 'SOGoParentFolder'. If it's a redundant call as I suspect, it will not make a difference. But if it is called, my changes will fix a method call from failing at runtime. Ideally this should be looked into more thoroughly. However my fix will clears the compiler warning and will not make anything worse than it is already.
NOTE: 'appendCollectedSources' does not exist anywhere else, even in SOPE.

[ethoms]

I adjusted the patch for 'SoObjects/Appointments/SOGoCalendarComponent.m' since I just noticed it had a semi-colon after the method declaration (before the method code). And added a useful comment.

[extrafu]

The appendCollectedSources change is incorrect.

To avoid the warning, we can do in the following code segment:

`

• (NSException *) initSubFolders
  {
  NSException *error;

  if (!subFolders)
  {
  subFolders = [NSMutableDictionary new];
  error = [self appendPersonalSources];
  if (!error)
  if ([self respondsToSelector:@selector(appendCollectedSources)])
  error = [self appendCollectedSources];
  if (!error)
  `

The line:
error = [self appendCollectedSources];
could be replaced with:
error = [self performSelector: @selector(appendCollectedSources)];

[ethoms]

Yes, that fixes it. I'll make the changes to the pull request.

I still don't understand though. If a method only exists in a subclass of me, how can I call it? In C/C++ this is just not possible. I'll have to read up on selectors, I'm learning Objective C just to maintain the FreeBSD SOPE/SOGo ports.