Period division for long occurrence lists

For each long list DDC stores so called period division, which is a list of integers X[1],X[2], ..X[M], where M is the number of corpus periods. All occurrences from X[i-1] until X[i] belongs to corpus period i. Generally, using this period division one can quickly get the sublist of occurrences which belongs to the same corpus period. All period divisions are written in CIndexSetForQueryingStage::m_EndPeriodOffsets .