This tries to propagate exceptions which are externally thrown into
external try-catch handlers before scheduling them. This also allows
embedders to nest external try-catch handlers.

R=rossberg@chromium.org
BUG=v8:2166
TEST=cctest/test-api/TryCatchNested

Review URL: https://chromiumcodereview.appspot.com/10555004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11834 ce2b1a6d-e550-0410-aec6-3dcde31c8c00