Do proper dispatch on declaration type instead of mingling together
different code generation paths. Once we add more declaration forms,
this is more scalable.

In separate steps, I'd like to (1) clean up the logic for DeclareGlobal,
and (2) try to reduce the special handling of the name function var if
possible.

R=fschneider@chromium.org
BUG=
TEST=

Review URL: https://chromiumcodereview.appspot.com/9704054

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11331 ce2b1a6d-e550-0410-aec6-3dcde31c8c00