[analyzer] Rename generateNode -> addTransition in CheckerContext

Also document addTransition methods.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@143059 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/StaticAnalyzer/Checkers/CastToStructChecker.cpp b/lib/StaticAnalyzer/Checkers/CastToStructChecker.cpp
index c855210..2a3da78 100644
--- a/lib/StaticAnalyzer/Checkers/CastToStructChecker.cpp
+++ b/lib/StaticAnalyzer/Checkers/CastToStructChecker.cpp
@@ -56,7 +56,7 @@
 
   // Now the cast-to-type is struct pointer, the original type is not void*.
   if (!OrigPointeeTy->isRecordType()) {
-    if (ExplodedNode *N = C.generateNode()) {
+    if (ExplodedNode *N = C.addTransition()) {
       if (!BT)
         BT.reset(new BuiltinBug("Cast from non-struct type to struct type",
                             "Casting a non-structure type to a structure type "