[Analyzer] Iterator Checker - Part 2: Increment, decrement operators and ahead-of...

[Analyzer] Iterator Checker - Part 2: Increment, decrement operators and ahead-of-begin checks

Add handling of the begin() funcion of containers to the iterator checkers,
together with the pre- and postfix ++ and -- operators of the iterators. This
makes possible the checking of iterators dereferenced ahead of the begin of the
container.

Differential Revision: https://reviews.llvm.org/D32642

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@335835 91177308-0d34-0410-b5e6-96231b3b80d8