document how to switch between branches when building JBT locally

(2012-01-16 12:09:33) maxandersen: nboldt: if I build parent and say jmx from trunk, then switch to branch it will pick that up if i'm not rebuilding everything.
12:10
(2012-01-16 12:10:11) nboldt: ah, true
(2012-01-16 12:10:32) nboldt: but that's an osgi issue
(2012-01-16 12:11:36) nboldt: eg., if tycho sees locally jmx_3.3.0.....Beta1 (built from trunk) and you switch to branch and rebuild something that needs jmx, it'll look at staging/composite/3.3.indigo/ site for a newer version of jmx (with M5 suffix) and compare that to your locally-build version
(2012-01-16 12:12:09) nboldt: I can't solve that w/ diffferent parent poms in nexus, even if they're differently versioned 3.3.M5 vs. 3.3.trunk
(2012-01-16 12:12:21) nboldt: instead of both having 0.0.3-SNAPSHOT
(2012-01-16 12:13:03) nboldt: the problem there is that your ~/.m2 cache contains a newer version of the plugin/feature than what's on the site from which upstream bits are sourced, so Tycho picks the local bits (and throws a warning in your build log)
(2012-01-16 12:13:25) maxandersen: that is not happening when building full via mvn - then it uses the local ones over the remote ones.
(2012-01-16 12:13:33) nboldt: so, yes, in that scenario, you DO have to nuke the ~/.m2 folder (or better, move it so you can have two versions of the ~/.m2 cache for trunk vs. branch)
(2012-01-16 12:13:58) nboldt: maxandersen: of course, because you asked it to rebuild locally from source rather than resolving from binary)
(2012-01-16 12:14:34) nboldt: so there are two workarounds to the "multiple component build dependencies across branch/trunk" – a) have two different ~/.m2 caches and switch them as you switch parent poms
(2012-01-16 12:14:50) nboldt: b) rebuild everything locally when you switch branches
12:15
(2012-01-16 12:15:23) nboldt: I feel like this should be documented somewhere