Fix for issue #8752 which, if merged, replaces PR #8757
I prepped functional/listsinceblock.py for additional tests. Wrote a test for the above issue. Made a fix to rpcwallet.cpp:listsinceblock(…).
The fix takes advantage of CMerkleTx::GetDepthInMainChain() returning a negative value for conflicted transactions. The negative value represents the depth of the transaction with which it is conflicted. Taking abs(…) of this lets us use the same logic for filtering un-conflicted transactions to filter the conflicted ones.