A few simple fixes and tweaks...

Hey, here's a basic summary:

1) Change when errors/warnings are cleared during a build... it was happening after validators ran and so I'd never see messages from BsnValidator.
2) Fix an NRE in BsnValidator just so a more helpful message shows up (sorry, unsure why build.getPropertiesFile() would be NULL here)
3) Be more conservative when we override trace from the ILaunchConfiguration... I was never checking that box and just trying to use -runtrace, which would never work because we check ILaunchConfiguration for a value and use false otherwise, so it'd always be false. This only copies the trace setting from ILC if it's been set. 

Lemme know if you'd like a different approach anywhere or if I need to fix styling, thanks!