Replace the 'unable_to_parse' key used in three places with three difference keys.
Provide three more informative and less ambiguous error messages in place of 'Parse error'.

Add three test/message cases to cover the new messages.

BUG=2636

Review URL: https://codereview.chromium.org/14161007

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@14462 ce2b1a6d-e550-0410-aec6-3dcde31c8c00