tail: fix inotify startup races

The previous fixes to races in the various tail tests,
identified actual races in the tail inotify implementation.
With --follow=descriptor, if the tailed file was replaced before
the inotify watch was added, then any subsequent changes were ignored.
Similarly in --follow=name mode, all changes to a new name were
effectively ignored if that name was created after the original open()
but before the inotify_add_watch().

* src/tail.c (tail_forever_inotify): Fix 3 cases.
1. With -f, don't stop tailing when file removed before watch.
2. With -f, watch right file when file replaced before watch.
3. With -F, inspect correct file when replaced before watch.
Existing tests identify these when tail compiled with TAIL_TEST_SLEEP.
* tests/tail-2/inotify-rotate-resources.sh:
This test also identifies the issue with --follow=name
when TAIL_TEST_SLEEP is used.  Adjust so the test is immune
to such races, and also fail quicker on remote file systems.
* tests/tail-2/inotify-race2.sh: A new test using GDB,
based on inotify-race.sh, which tests the -F race
without needed recompilation with sleeps.
* tests/local.mk: Reference the new test.
* NEWS: Mention the bug.

NEWS

@@ -45,6 +45,10 @@ GNU coreutils NEWS                                    -*- outline -*-
   tail -f again follows changes to a file after it's renamed.
   [bug introduced in coreutils-7.5]
 
+  tail --follow no longer misses changes to files if those files were
+  replaced before inotify watches were created.
+  [bug introduced in coreutils-7.5]
+
 ** New features
 
   chroot accepts the new --skip-chdir option to not change the working directory