Add an alternate transaction journal with higher throughput (nio / java.util.concurrent based).

I found BTM a few weeks ago when I was looking for a replacement for c3p0 (which caused deadlocks) and really like it for it's simplicity and stability. When I saw BTM, I thought that JTA is even better for my Spring/Infinispan/Jpa based app anyway.

All is stable now and fine until I switched from 'NullJournal' to 'DiskJournal'. The TX/s dropped to 1/10 of the values they've been before and I started thinking whether a disk journal should really drop performance so much... luckily BTM allows to create-your-own so I started to create a proof of concept.

Attached is the compiled binary and a patch to the version currently in 'GIT' (actually only the parent pom is changed as the rest is simply a separate module). Built on my machine I got the following figures when running the unit tests:

• DiskJournal: 12850 transactions, took 51,12 seconds (251,39 tx/s)
• NioJournal (w. fsync): 257000 transactions, took 5,51 seconds (46667,88 tx/s)
• NioJournal (w/o. fsync): 257000 transactions, took 1,43 seconds (179344,03 tx/s)
• NullJournal (reference): 257000 transactions, took 0,20 seconds (1266009,85 tx/s)

(Implementation class of the attached JAR is 'bitronix.tm.journal.nio.NioJournal')

What I sent is a first working prototype and should really be considered experimental (license is Apache2 but can be changed to LGPL). Better test coverage and additional log output is pending. However I would appreciate the inclusion of the code and would be happy to continue working on this module if this is OK with you the lead .

If you accept this it would probably be great to extract an abstract base class out of 'TransactionLogRecord' that contains only those entries that a Recoverer needs, so that I don't need to store values that have no use for the NIO journal.