[analyzer] Rename generateNode -> addTransition in CheckerContext

Also document addTransition methods.

llvm-svn: 143059
diff --git a/clang/lib/StaticAnalyzer/Checkers/PointerSubChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/PointerSubChecker.cpp
index 924c7f2..5e5e3e3 100644
--- a/clang/lib/StaticAnalyzer/Checkers/PointerSubChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/PointerSubChecker.cpp
@@ -59,7 +59,7 @@
   if (isa<SymbolicRegion>(BaseLR) || isa<SymbolicRegion>(BaseRR))
     return;
 
-  if (ExplodedNode *N = C.generateNode()) {
+  if (ExplodedNode *N = C.addTransition()) {
     if (!BT)
       BT.reset(new BuiltinBug("Pointer subtraction", 
                           "Subtraction of two pointers that do not point to "