Slow Performance of Qt lists and trees

When lists/ tables are used with about 500000 to 2000000 items in it and items has to be displayed in a selective manner, it is unexpectedly slow in Qt 4.x. In Qt 3.x it has not been the case. Following attached code improves this selection code significantly and will be a good addition to Qt 5.0 When Released.

Instructions to run the code.
«#define SELECT_WITH_OUT_MERGE 1» . Uncomment it to run the test using selectEx instead of QItemSelection ::select. It works much more faster with selectEx.