The original implementation of pg_verify_checksums used a blacklist to
decide which files should be skipped for scanning as they do not include
data checksums, like pg_internal.init or pg_control.  However, this
missed two things:
- Some files are created within builds of EXEC_BACKEND and these were
not listed, causing failures on Windows.
- Extensions may create custom files in data folders, causing the tool
to equally fail.

This commit switches to a whitelist-like method instead by checking if
the files to scan are authorized relation files.  This is close to a
reverse-engineering of what is defined in relpath.c in charge of
building the relation paths, and we could consider refactoring what this
patch does so as all routines are in a single place.  This is left for
later.

This is based on a suggestion from Andres Freund.  TAP tests are updated
so as multiple file patterns are tested.  The bug has been spotted by
various buildfarm members as a result of b34e84f1 which has introduced
the TAP tests of pg_verify_checksums.

Author: Michael Paquier
Reviewed-by: Andrew Dunstan, Michael Banck
Discussion: https://postgr.es/m/20181012005614.GC26424@paquier.xyz
Backpatch-through: 11