The registers now have memory and stay expanded

The registers now have memory and stay expanded

* Source/DebuggerWindowController.h: expandedRegisters is now an NSMutableSet
* Source/DebuggerWindowController.m:
([DebuggerWindowController initWithPort:session:]): Change allocated type of expandedRegisters
([DebuggerWindowController setRegister:]): Finished logic for expanding remembered registers
([DebuggerWindowController outlineViewItemDidExpand:]): Use the "fullname" attribute to get the full variable name so scope is accounted for in expanded memory
([DebuggerWindowController outlineViewItemDidCollapse:]): ditto
* Source/NSXMLElementAdditions.h:
* Source/NSXMLElementAdditions.m:
([NSXMLElement(NSXMLElementAdditions) fullname]): New method