Add vars to compile plugin debug info about joda-time

[jodastephen]

Why do you need this?

[miptalan]

Stephen, having only lines and source makes debugging inside Joda-time library pretty useless - yes, I can step through code, but vars should still be calculated on paper. Vars add almost negligible overhead, but give a huge benefit for any contributor/curious mind.

[jodastephen]

The overhead is from 576K to 643K, certainly not negligible. Given I've had complaints about the size of the jar in the past, I'm not motivated to make such an increase (and thats why they were omitted originally).