pgsql: Check for tabs in postgresql.conf.sample.

Check for tabs in postgresql.conf.sample.

The previous commit updated this file to use spaces instead of
tabs.  This commit adds a test to ensure that no new tabs are
added.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Discussion: https://postgr.es/m/aReNUKdMgKxLqmq7%40nathan

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/379f0e9f72b3e2504641aaabc7db2b03c00b146b

Modified Files
--------------
src/test/modules/test_misc/t/003_check_guc.pl | 14 ++++++++++++++
1 file changed, 14 insertions(+)