Log Message:
p5-Coro: update to 6.57.

Still works as badly as before:
t/00_basic.t .... Failed 3/5 subtests
t/01_unblock.t .. Failed 8/12 subtests

6.57  Wed Jul 29 15:08:44 CEST 2020
	- override AnyEvent condvar methods "properly", as AnyEvent
          has support for pluggable condvars since 2011. This also
          avoids problems with recursive waits by avoiding to mix
          impl methods with coro code.
	- allow rouse_wait to be called in a different thread.
        - slightly clarify rouse_cb/rouse_wait documentation.
	- slightly improve rouse callback performance and memory usage.
        - try to report correct calller when throwing exception in
          on $condvar->recv, not a useless line in Coro::AnyEvent.

6.56  Thu Feb 20 19:40:07 CET 2020
	- Coro::EV::time*once functions used ev_once, which is not cancelable.
          This could cause problems due to I/O watchers not being stopped up
          on exceptions/cancellation.

6.55  Fri Jul 19 17:28:09 CEST 2019
	- Coro::RWLock woke up only one reader instead of all after a wrlock
          (analyzed and patch by Maxim Skorobogatov).
        - slightly improved documentation of Coro::RWLock and RWLock testcase.
        - quickly (re)-ported to minix 3.3 before minix crashed again.