Fix how YAML I/O detects flow sequences.  
Update test case to verify flow sequence is
written as a flow sequence.

llvm-svn: 171514
diff --git a/llvm/lib/Support/YAMLTraits.cpp b/llvm/lib/Support/YAMLTraits.cpp
index 8fcef40..ef3948d 100644
--- a/llvm/lib/Support/YAMLTraits.cpp
+++ b/llvm/lib/Support/YAMLTraits.cpp
@@ -411,8 +411,8 @@
 }
 
 unsigned Output::beginFlowSequence() {
-  this->newLineCheck();
   StateStack.push_back(inFlowSeq);
+  this->newLineCheck();
   ColumnAtFlowStart = Column;
   output("[ ");
   NeedFlowSequenceComma = false;