Move code for code generator static member functions, code generation

functions on AST nodes, and helper class member functions (eg, stub
classes) toward the bottom of the codegen*.cc files.  The macro __ is
now #define'd exactly twice and #undef'd twice.
Review URL: http://codereview.chromium.org/6075

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@409 ce2b1a6d-e550-0410-aec6-3dcde31c8c00