[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/UnixAPIChecker.cpp b/lib/StaticAnalyzer/Checkers/UnixAPIChecker.cpp
index 87f532a..cec286d 100644
--- a/lib/StaticAnalyzer/Checkers/UnixAPIChecker.cpp
+++ b/lib/StaticAnalyzer/Checkers/UnixAPIChecker.cpp
@@ -215,7 +215,7 @@
   // Assume the the value is non-zero going forward.
   assert(trueState);
   if (trueState != state) {
-    C.generateNode(trueState);
+    C.addTransition(trueState);
   }
 }