IB:
* removed CONCURR_TRX from VTQ;
* new fields in VTQ: COMMIT_ID, ISO_LEVEL.

SQL:
* renamed BEGIN_TS, COMMIT_TS to VTQ_BEGIN_TS, VTQ_COMMIT_TS;
* new functions: VTQ_COMMIT_ID, VTQ_ISO_LEVEL, VTQ_TRX_ID, VTQ_TRX_SEES, VTQ_TRX_SEES_EQ;
* versioned SELECT for IB uses VTQ_TRX_SEES, VTQ_TRX_SEES_EQ.

Closes #71