Emit idle event after Libevent2Driver.processEvents - fixes hanging tasks.

Tasks didn't run at all in applications that used only processEvents() and neither runEventLoop(), nor runEventLoopOnce().
Emit idle events also for Win32Driver.processEvents.
Fixing Path.relativeTo for directories, a Path whith endsWithSlash==true had this property stripped, when made relative to another Path.
Merge branch 'master' of https://github.com/rejectedsoftware/vibe.d