Cleanup sendToClient and add rsGetDt().
Remove legacy implemtation of matrix calls which were moved to llvm bc.

Change-Id: I527740590067db3bcb2147233ef41fb057f1d2a8
diff --git a/rsContext.cpp b/rsContext.cpp
index d6df581..d1784f3 100644
--- a/rsContext.cpp
+++ b/rsContext.cpp
@@ -780,9 +780,13 @@
         }
     }
     //LOGE("sendMessageToClient 2");
-    void *p = mIO.mToClient.reserve(len);
-    memcpy(p, data, len);
-    mIO.mToClient.commit(cmdID, len);
+    if (len > 0) {
+        void *p = mIO.mToClient.reserve(len);
+        memcpy(p, data, len);
+        mIO.mToClient.commit(cmdID, len);
+    } else {
+        mIO.mToClient.commit(cmdID, 0);
+    }
     //LOGE("sendMessageToClient 3");
     return true;
 }