new design discussed on cfe-dev, with further steps in that direction to come.
It is already much more complete than the previous visitor.
Patch by Zhanyong and Craig with 80 column wraps and one missing declaration
added by me.
llvm-svn: 105709
walk an entire AST, including all of the types, declarations,
statements, and expressions, and allowing one to easily override the
behavior of the walk at any particular node kind.
llvm-svn: 103308
