Shut down all named pipes and tcp streams in jl_close_uv.
Add a test for shutdown being called twice.  Unfortunately it hangs rather than fails.
Stop using libuv's flags, check in jl_close_uv if close has already been called from julia
Change is_open to isopen
Test handle type before testing writable
If a shutdownable stream is not writable, don't call uv_close on it.
Get jl_uv_close working again by checking uv_is_closing at the top and closing when a handle isn't writable or closing
Use JULIA_CB to cache isopen
Merge pull request #3084 from rsofaer/uv_shutdown_in_julia_close

RFC: uv_shutdown in julia close