Fix issue with openfiles= and file sizing

Fill the given size as well as we can, given the size and nr
of files.

Fix an issue where we don't properly honor how many files to
keep open at any point in time.

Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/file.h b/file.h
index d7e05f4..19413fc 100644
--- a/file.h
+++ b/file.h
@@ -176,5 +176,6 @@
 extern int get_fileno(struct thread_data *, const char *);
 extern void free_release_files(struct thread_data *);
 void fio_file_reset(struct thread_data *, struct fio_file *);
+int fio_files_done(struct thread_data *);
 
 #endif