Trying to get the register viewer to work

Trying to get the register viewer to work

* Source/NSXMLElementAdditions.m: New category that provides access to attributes that NSTreeController can't access
* MacGDBp.xcodeproj: Added NSXMLElementAdditions.m
* Source/DebuggerConnection.m:
([DebuggerConnection dataReceived:deliverTo:]): Print out the data we're receiving to make debugging easier
([DebuggerConnection updateStackTraceAndRegisters:]): Send the context_get command and receive the data
([DebuggerConnection registerReceived:]): New method to handle the received register packet
* Source/DebuggerWindowController.m|h: Added _register and a setter for it
([DebuggerWindowController setRegister:]): New method
* English.lproj/Debugger.nib: Added a tree controller and tried to hook it up properly