When D8 is used as remote debugger the command 'break' (shorthand 'b') can be used to break JavaScript execution.

Fixed the printing of the prompt 'dbg>' and printing of error messages.
Review URL: http://codereview.chromium.org/1566049

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4437 ce2b1a6d-e550-0410-aec6-3dcde31c8c00