Commit confirmation fails on blockchain reorg

[elv-serban]

Blockchain reorgs may cause a given block to appear at a given number but end up at an earlier number. In that case the client needs to check back several blocks.

Example:

"Querying contract events 0xa6775495af7913a1d7a2e829451a20c9f326bc55 - Blocks 32842906 to 32843905"

The confirmation comes one block earlier.