[QtScript/JavaScriptCore] Make QScriptEngineAgent callbacks work

Patches:
Add QtScript-specific callbacks to Debugger: http://gitorious.org/+qtwebkit-developers/qtwebkit/qtwebkit-qtscript-integration/commit/ac2a0797bce3fde23c411f8ad7602dee994a635e
Add QtScript-specific Debugger callbacks (Interpreter mode): http://gitorious.org/+qtwebkit-developers/qtwebkit/qtwebkit-qtscript-integration/commit/088e4963bc89f0f113a5929346fe25047f63f845
Add QtScript-specific Debugger callbacks (JIT mode): http://gitorious.org/+qtwebkit-developers/qtwebkit/qtwebkit-qtscript-integration/commit/57faaf7b35cef9f97e6068a102c7ba7b7a02217c

Reason: Without these patches, QScriptEngineAgent callbacks don't behave as in the old QtScript implementation. Without this precise behavior, you can't debug QtScript (e.g. QScriptEngineDebugger would break).

Patches are needed both for interpreter and JIT, and they can be a nuisance to rebase.
Additionally, JSC would like to move away from this debugging model, so it's likely that the JSC::Debugger class will go away eventually.

Proposed action: Postpone.