Log Message:
libev: update to 4.27.

4.27 Thu Jun 27 22:43:44 CEST 2019
	- linux aio backend almost complete rewritten to work around its
          limitations.
        - epoll backend now mandatory for linux aio backend.
        - fail assertions more aggressively on invalid fd's detected
          in the event loop, do not just silently fd_kill in case of
          user error.
        - ev_io_start/ev_io_stop now verify the watcher fd using
          a syscall when EV_VERIFY is 2 or higher.

4.26 (EV only)
	- update to libecb 0x00010006.
	- new experimental linux aio backend (linux 4.18+).
	- removed redundant 0-ptr check in ev_once.
        - updated/extended ev_set_allocator documentation.
        - replaced EMPTY2 macro by array_needsize_noinit.
        - minor code cleanups.
        - epoll backend now uses epoll_create1 also after fork.