[Firebird-net-provider] Calling BeginTransaction multiple times

[Jojakim S. <JS...@de...>]

Hello!

A got the new CVS version and had problems to call
FbConnection.BeginTransaction() a second time after disposing the
FbTransaction-object returned by the first call.
I studied code and found that FbTransaction.Dispose() doesn't reset the
active transaction object of the connection. Due to the simple test for
activeTxn != null when calling FbConnection.BeginTransaction() the second
call throws.

I added an internal property to FbTransaction to query the transactions
state and extended the test in FbConnection.BeginTransaction() to check the
state.

-- Joja