Enhance exception throwing with Boost Exception library

Change-Id: I471023fc23ffaebe04d9668426b4c1b03e4962ba
Refs: #2997
diff --git a/src/util/digest.cpp b/src/util/digest.cpp
index d5bb312..23af4c9 100644
--- a/src/util/digest.cpp
+++ b/src/util/digest.cpp
@@ -126,7 +126,7 @@
 {
   // cannot update Digest when it has been finalized
   if (m_isFinalized)
-    throw Error("Digest has been already finalized");
+    BOOST_THROW_EXCEPTION(Error("Digest has been already finalized"));
 
   m_hash.Update(buffer, size);