[JMeter] release 2.5.1 to fix issues in 2.5?

I'm thinking it might be worth releasing 2.5.1 soon.

The main reason is to fix the bug in HttpClient4 connection handling,
but there have been a few other useful fixes.

What do you think?

If there are any quick fix bugs we can squash, let's do those (e.g.
I've nearly finished on Bug 48943), but more resistant bugs could be
left for a later release.