catch panic within transaction to complete rollback (fixes #748)

[sio4]

Connection.Transaction() starts a transaction before executing a given inner function and then commits or rollback the transaction controlled by the return error value of the inner function. However, as reported in #748, it just exits without committing or rolling back the current transaction so the transaction (and lock status) could remain as open (it could depend on the behavior of the backing database engine).

The current behavior of the method is:

=== RUN   Test_Connection_Transaction
[POP] 2022/09/22 20:08:51 sql - --- BEGIN Transaction ---
--- FAIL: Test_Connection_Transaction (0.00s)
panic: handler panic [recovered]
	panic: handler panic
<...>

The fixed behavior by this PR is:

=== RUN   Test_Connection_Transaction
[POP] 2022/09/22 20:11:01 sql - --- BEGIN Transaction ---
[POP] 2022/09/22 20:11:01 sql - --- ROLLBACK Transaction (inner function panic) 

Additionally, this PR added log(logging.SQL,...) for begin, commit, and rollback actions so the transaction status could be easily observed along with SQL statements when the user enabled SQL logging.

fixes #748

[sio4]

comment on the code