fsmonitor: return invalidated cache-entry count on non-directory event

fsmonitor: return invalidated cache-entry count on non-directory event

Teach the refresh callback helper function for unqualified FSEvents
(pathnames without a trailing slash) to return the number of
cache-entries that were invalided in response to the event.

This will be used in a later commit to help determine if the observed
pathname was (possibly) case-incorrect when (on a case-insensitive
file system).

Signed-off-by: Jeff Hostetler <jeffhostetler@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>