Fix external exceptions in external try-catch handlers.

Fix external exceptions in external try-catch handlers.

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.

This just relands r11834.

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

Committed: http://code.google.com/p/v8/source/detail?r=13129

[Sven Panne, 2012-12-04 10:35:09]

lgtm