Ruby: Add new object called WireBuffer to mimic a Wire.

This is a substitute for MessageBuffers between controllers where you don't
want messages to actually go through the Network, because requests/responses can
always get reordered wrt to one another (even if you turn off Randomization and turn on Ordered)
because you are, after all, going through a network with contention. For systems where you model
multiple controllers that are very tightly coupled and do not actually go through a network,
it is a pain to have to write a coherence protocol to account for mixed up request/response orderings
despite the fact that it's completely unrealistic.  This is *not* meant as a substitute for real
MessageBuffers when messages do in fact go over a network.

src/mem/ruby/system/SConscript

@@ -37,6 +37,7 @@ SimObject('Cache.py')
 SimObject('Sequencer.py')
 SimObject('DirectoryMemory.py')
 SimObject('MemoryControl.py')
+SimObject('WireBuffer.py')
 SimObject('RubySystem.py')
 
 Source('DMASequencer.cc')
@@ -44,6 +45,7 @@ Source('DirectoryMemory.cc')
 Source('SparseMemory.cc')
 Source('CacheMemory.cc')
 Source('MemoryControl.cc')
+Source('WireBuffer.cc')
 Source('MemoryNode.cc')
 Source('PersistentTable.cc')
 Source('RubyPort.cc')