pgsql: Handle concatenated gzip members in astreamer decompressor

Handle concatenated gzip members in astreamer decompressor

With WAL streaming, pg_basebackup -Ft -z writes pg_wal.tar.gz as a
series of gzip members. The decompressor did not reset the inflate
state when one ended, so inflate consumed nothing more and the loop
never finished. This caused pg_waldump to hang on such backups and
as a consequence pg_verifybackup (which use pg_waldump) would hang.

A test is added to pg_verifybackup for checking a gzip-compressed
tar backup, which in turn will verify that pg_waldump works.

Author: Shihao Zhong <zhong950419(at)gmail(dot)com>
Reviewed-by: Daniel Gustafsson <daniel(at)yesql(dot)se>
Reviewed-by: Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com>
Reviewed-by: Andrew Dunstan <andrew(at)dunslane(dot)net>
Discussion: https://postgr.es/m/CAGRkXqTcyuog_MzKqQm+am2xMefLFJTSKaRevnfypDWirCFvdA@mail.gmail.com
Backpatch-through: 19

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/f884f359f5acb29bd423001b4878b85f51406b42

Modified Files
--------------
src/bin/pg_verifybackup/t/007_wal.pl | 22 ++++++++++++++++++++++
src/fe_utils/astreamer_gzip.c | 8 ++++++++
2 files changed, 30 insertions(+)