Make JIT dump file to be found in extra_images::locate_image() method.
https://github.com/ChangbinPark/Oprofile/issues/3
JIT dump object in session directory can't be loaded in opreport
when "--root" option is given, and given "root path" doesn't contains
JIT dump object within its child.
In such a case, JIT dump object is requested to extra_images::locate_image()
method with real path of it.
This patch detect such a case and check it loadable.