Fix clang's use of DenseMap iterators after r86636 fixed their constness.
Patch by Victor Zverovich!

llvm-svn: 86638
diff --git a/clang/lib/Analysis/ExplodedGraph.cpp b/clang/lib/Analysis/ExplodedGraph.cpp
index 0dc81a4..3b339ff 100644
--- a/clang/lib/Analysis/ExplodedGraph.cpp
+++ b/clang/lib/Analysis/ExplodedGraph.cpp
@@ -273,7 +273,7 @@
 
 ExplodedNode*
 InterExplodedGraphMap::getMappedNode(const ExplodedNode* N) const {
-  llvm::DenseMap<const ExplodedNode*, ExplodedNode*>::iterator I =
+  llvm::DenseMap<const ExplodedNode*, ExplodedNode*>::const_iterator I =
     M.find(N);
 
   return I == M.end() ? 0 : I->second;