Deprecate QScriptContextInfo

http://doc.trolltech.com/4.7/qscriptcontextinfo.html

This is a low-level class. These are the known use cases:

• Constructing a backtrace. This class gives access to the individual components that make up the backtrace (fileName(), lineNumber(), functionName()), so that e.g. a graphical debugger can arrange these nicely. Used in combination with QScriptContext::parentContext() to walk up the QtScript stack.
• Finding out where a native function was called from. This can be done by creating a QScriptContextInfo for the parentContext(). This is useful for test tools (QTestLib integration) and loggers.

Having a backtrace() function in QScriptEngine that returns a list of frame info structures can handle both of the above use cases.