Ignore kqueue errors on removed entries

[ghost]

When the BSD adapter decides it will watch a new file, it may happen
that the file was already removed when the call to watch this file
actually happens, raising Errno::ENOENT exception.

As a workaround, we rescue this specific error and log a warning, in
case of a more serious issue than just an ephemeral file.

Exception example:

E, [2015-03-14T20:07:52.726600 #2299] ERROR -- : run() in thread failed: No such file or directory - Failed to open file /.../src/my/listen-kqueue/tmp/toto: File doesn't exist.:/.../.gem/ruby/22/gems/rb-kqueue-0.2.3/lib/rb-kqueue/watcher/file.rb:19:in `initialize'
/.../.gem/ruby/22/gems/rb-kqueue-0.2.3/lib/rb-kqueue/queue.rb:227:in `new'
/.../.gem/ruby/22/gems/rb-kqueue-0.2.3/lib/rb-kqueue/queue.rb:227:in `watch_file'
/.../src/sys/listen/lib/listen/adapter/bsd.rb:96:in `_watch_file'
/.../src/sys/listen/lib/listen/adapter/bsd.rb:89:in `block in _watch_for_new_file'
/usr/local/lib/ruby/2.2/find.rb:48:in `block (2 levels) in find'
/usr/local/lib/ruby/2.2/find.rb:47:in `catch'
/usr/local/lib/ruby/2.2/find.rb:47:in `block in find'
/usr/local/lib/ruby/2.2/find.rb:42:in `each'
/usr/local/lib/ruby/2.2/find.rb:42:in `find'
/.../src/sys/listen/lib/listen/adapter/bsd.rb:103:in `_find'
/.../src/sys/listen/lib/listen/adapter/bsd.rb:87:in `_watch_for_new_file'
/.../src/sys/listen/lib/listen/adapter/bsd.rb:68:in `_process_event'
/.../src/sys/listen/lib/listen/adapter/base.rb:47:in `block (2 levels) in configure'
/.../.gem/ruby/22/gems/rb-kqueue-0.2.3/lib/rb-kqueue/watcher.rb:90:in `call'
/.../.gem/ruby/22/gems/rb-kqueue-0.2.3/lib/rb-kqueue/watcher.rb:90:in `callback!'
/.../.gem/ruby/22/gems/rb-kqueue-0.2.3/lib/rb-kqueue/event.rb:80:in `callback!'
/.../.gem/ruby/22/gems/rb-kqueue-0.2.3/lib/rb-kqueue/queue.rb:337:in `block in process'
/.../.gem/ruby/22/gems/rb-kqueue-0.2.3/lib/rb-kqueue/queue.rb:337:in `each'
/.../.gem/ruby/22/gems/rb-kqueue-0.2.3/lib/rb-kqueue/queue.rb:337:in `process'
/.../.gem/ruby/22/gems/rb-kqueue-0.2.3/lib/rb-kqueue/queue.rb:316:in `run'
/.../src/sys/listen/lib/listen/adapter/bsd.rb:50:in `_run'
/.../src/sys/listen/lib/listen/adapter/base.rb:58:in `block in start'
/.../src/sys/listen/lib/listen/internals/thread_pool.rb:7:in `call'
/.../src/sys/listen/lib/listen/internals/thread_pool.rb:7:in `block in add'

Warning example, with this change:

W, [2015-03-14T20:21:16.209281 #5997]  WARN -- : kqueue: watch file failed: No such file or directory - Failed to open file /.../src/my/listen-kqueue/tmp/toto: File doesn't exist.
I, [2015-03-14T20:21:16.313068 #5997]  INFO -- : listen: raw changes: [[:removed, "/.../src/my/listen-kqueue/tmp/toto"]]
I, [2015-03-14T20:21:16.313146 #5997]  INFO -- : listen: final changes: {:modified=>[], :added=>[], :removed=>["/.../src/my/listen-kqueue/tmp/toto"]}
[…]

[e2]

Done. Thanks for investigating and testing!