Command-line jsc's exception handling should be rationalized

Command-line jsc's exception handling should be rationalized
https://bugs.webkit.org/show_bug.cgi?id=83437

Reviewed by Dan Bernstein.

- If an exception is thrown during run() execution, it is now propagated,
  so that it will terminate program execution unless it is caught.

- If program execution terminates with an exception, the exception is now
  always printed.

- When printing the exception, the backtrace is now also printed if one is
  available. It will only not be available if you use something akin to my
  favorite line of code, 'throw "error"', since primitives don't have
  properties and hence we cannot attach a "stack" property to them.

* jsc.cpp:
(functionRun):
(runWithScripts):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@113553 268f45cc-cd09-0410-ab3c-d52691b4dbfc