Reviewed by Maciej and Geoff.

        http://bugzilla.opendarwin.org/show_bug.cgi?id=7080
        Provide some way to stop a JavaScript infinite loop
        
        * kjs/completion.h:
        (KJS::):
        Add Interrupted completion type.
        
        * kjs/function.cpp:
        (KJS::FunctionImp::callAsFunction):
        (KJS::GlobalFuncImp::callAsFunction):
        Only set the exception on the new ExecState if the current one has had one.
        
        * kjs/interpreter.cpp:
        (KJS::TimeoutChecker::startTimeoutCheck):
        (KJS::TimeoutChecker::stopTimeoutCheck):
        (KJS::TimeoutChecker::alarmHandler):
        (KJS::TimeoutChecker::pauseTimeoutCheck):
        (KJS::TimeoutChecker::resumeTimeoutCheck):
        New TimeoutChecker class which handles setting Interpreter::m_timedOut flag after a given
        period of time. This currently only works on Unix platforms where setitimer and signals are used.
        
        (KJS::Interpreter::Interpreter):
        Initialize new member variables.
        
        (KJS::Interpreter::~Interpreter):
        Destroy the timeout checker.
        
        (KJS::Interpreter::startTimeoutCheck):
        (KJS::Interpreter::stopTimeoutCheck):
        (KJS::Interpreter::pauseTimeoutCheck):
        (KJS::Interpreter::resumeTimeoutCheck):
        Call the timeout checker.
        
        (KJS::Interpreter::handleTimeout):
        Called on timeout. Resets the m_timedOut flag and calls shouldInterruptScript.
        
        * kjs/interpreter.h:
        (KJS::Interpreter::setTimeoutTime):
        New function for setting the timeout time.
        
        (KJS::Interpreter::shouldInterruptScript):
        New function. The idea is that this should be overridden by subclasses in order to for example
        pop up a dialog asking the user if the script should be interrupted.
        
        (KJS::Interpreter::checkTimeout):
        New function which checks the m_timedOut flag and calls handleTimeout if it's set.
        
        * kjs/nodes.cpp:
        (DoWhileNode::execute):
        (WhileNode::execute):
        (ForNode::execute):
        Call Interpreter::checkTimeout after each iteration of the loop.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@14893 268f45cc-cd09-0410-ab3c-d52691b4dbfc