ReadIncOperation Class: propagation in apply_wprimew_order method

[hengxin]

Problem:

When W'WR order is applied, BFS framework is adopted for propagation. The Flag isCovered in ReadIncOperation should be reset (to false) after BFS procedure for reuse.

Solution:

Put all the ReadIncOperation(s) in a Set collection, then reset them just after the BFS procedure.

Possible Enhancement:

find out an appropriate opportunity to reset them, avoiding iteration over Set.