[analyzer] Malloc: A pointer might escape through CFContainers APIs,

funopen, setvbuf.

Teach the checker and the engine about these APIs to resolve malloc
false positives. As I am adding more of these APIs, it is clear that all
this should be factored out into a separate callback (for example,
region escapes). Malloc, KeyChainAPI and RetainRelease checkers could
all use it.

llvm-svn: 151737