Restart BackgroundPsql's timer more nicely.

Restart BackgroundPsql's timer more nicely.

Use BackgroundPsql's published API for automatically restarting
its timer for each query, rather than manually reaching into it
to achieve the same thing.

010_tab_completion.pl's logic for this predates the invention
of BackgroundPsql (and 664d75753 missed the opportunity to
make it cleaner).  030_pager.pl copied-and-pasted the code.

Author: Daniel Gustafsson <daniel@yesql.se>
Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi>
Reviewed-by: Andrew Dunstan <andrew@dunslane.net>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/1100715.1712265845@sss.pgh.pa.us