V2 llmessage merge, incl. llcommon requisites.

Excluded llareslistener, as that appears to only be present for unit-testing
Excluded new SSL methods because, well, they don't work right reliably in v2 for me

indra/llmessage/llxfer.cpp

@@ -74,6 +74,7 @@ void LLXfer::init (S32 chunk_size)
 	
 	mCallback = NULL;
 	mCallbackDataHandle = NULL;
+	mCallbackResult = 0;
 
 	mBufferContainsEOF = FALSE;
 	mBuffer = NULL;