Compiler warnings building GNUstep gui

[Fred Kiefer]

I am currently trying to reduce the amount of compiler warnings
generated by GNUstep gui. At the moment I have these left with a gcc
4.4.1 on a 64 bit system:

NSDocumentController.m:105: warning: ‘TypeInfoForHumanReadableName’
defined but not used
NSGraphicsContext.m: In function ‘-[NSGraphicsContext setFocusStack:]’:
NSGraphicsContext.m:379: warning: invalid receiver type ‘void *’
NSRulerMarker.m: In function ‘-[NSRulerMarker setRepresentedObject:]’:
NSRulerMarker.m:189: warning: ‘-retain’ not found in protocol(s)
NSSpellChecker.m: In function ‘-[NSSpellChecker _switchDictionary:]’:
NSSpellChecker.m:653: warning: ‘-retain’ not found in protocol(s)
NSSplitView.m: In function ‘-[NSSplitView mouseDown:]’:
NSSplitView.m:404: warning: ‘op.y’ may be used uninitialized in this
function
NSSplitView.m:404: warning: ‘op.x’ may be used uninitialized in this
function
IMLoading.m:215: warning: ‘__dummyFunctionForLinking’ defined but not used

All of these are definitely harmless and more a compiler issue than
problematic code. Still it would be nice to get rid of them in a clean
way. (That is without hiding potential problems in the future)

If you are getting other problems reported on different machines or with
an older (or newer?) compiler, I would like to take care of these too.

Fred