Further fixups to inotify setup

The last commits on this were somewhat broken and disabled inotify
  in general.  This should clean things up both with the detection
  and notification of runtime-disabled inotify for any initial
  failure reasons.
There's also some behavior change here.  Previous iterations of this
  code only intended to permanently disable inotify due to initial
  version check failure or ENOSYS, but other initial inotify setup
  failures would be treated the same as runtime inotify failures
  (which means periodic attempts to re-initialize inotify during
  manual directory scans without losing events).
The new code permanently runtime-disables inotify support on *any*
  variety of failure in the intial inotify setup calls.  Later
  runtime failures still result in periodic attempts to
  re-initialize inotify.
Normalize cpp feature flags to definedness rather than boolean value
Report compile-time features in help output