psql: set SHELL_ERROR and SHELL_EXIT_CODE in more places.

psql: set SHELL_ERROR and SHELL_EXIT_CODE in more places.

Make the \g, \o, \w, and \copy commands set these variables
when closing a pipe.  We missed doing this in commit b0d8f2d98,
but it seems like a good idea.

There are some remaining places in psql that intentionally don't
update these variables after running a child program:
	* pager invocations
	* backtick evaluation within a prompt
	* \e (edit query buffer)

Corey Huinker and Tom Lane

Discussion: https://postgr.es/m/CADkLM=eSKwRGF-rnRqhtBORRtL49QsjcVUCa-kLxKTqxypsakw@mail.gmail.com