Eliminate the LocalType enum in favor of a pair of functions, one for var
and const declarations and one for parameters.  Move the responsibility for
adding a parameter variable to the Scope's internal data structure into the
Scope and out of the parser.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8091 ce2b1a6d-e550-0410-aec6-3dcde31c8c00