blackbox: resurrect recursion guard If I added ui.log() to hg.repository() function, test-merge-subrepos.t exploded. The problem is that the blackbox may create new repository instance while logging is active, and the created repository owns its new ui derived from the baseui, not from the ui which is processing the active logging. I tried to work around the issue in ui.log(), but that turned out to be not easy. We shouldn't globally lock the ui.log() since there may be more than one active repo/ui instances in threaded environment. We could store the logging state in thread-local storage, but that seems unnecessarily complex. So this patch reintroduces the _inlog flag to per-repository logger instances.