0.6dev: Fixing numerous problems related to `BuildQueue.should_delete_build()`: * Crash when trying to write `TargetPlatform().name` to log when a target platform may no longer exist (#212, #391). * Delete pending builds that have a platform that is since deleted (#212, thanks dabrahams). * When not `build_all` delete pending builds if a newer build already exists (#264, thanks J?r?me Berger). This adds `min_rev_time` and `max_rev_time` criteria to `Build.select()` to enable time-based selection of builds. * Remove old-style logging as none of the nice log messages actually ended up in the environment log. Added 4 tests for each of the checks performed in `BuildQueue.should_delete_build()`.