Introduce separate maps for function and with contexts.  Use the function
context map for testing whether a context is a function context (global
contexts are no longer function contexts).

Split the paths for allocating with and catch contexts.

Rename some functions.  Generally refactor code to make it simpler.

R=ager@chromium.org
BUG=
TEST=

Review URL: http://codereview.chromium.org/7003058

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8231 ce2b1a6d-e550-0410-aec6-3dcde31c8c00