pgsql: Allow pg_basebackup to stream transaction log in tar mode

Allow pg_basebackup to stream transaction log in tar mode

This will write the received transaction log into a file called
pg_wal.tar(.gz) next to the other tarfiles instead of writing it to
base.tar. When using fetch mode, the transaction log is still written to
base.tar like before, and when used against a pre-10 server, the file
is named pg_xlog.tar.

To do this, implement a new concept of a "walmethod", which is
responsible for writing the WAL. Two implementations exist, one that
writes to a plain directory (which is also used by pg_receivexlog) and
one that writes to a tar file with optional compression.

Reviewed by Michael Paquier

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/56c7d8d4552180fd66fe48423bb2a9bb767c2d87

Modified Files
--------------
doc/src/sgml/ref/pg_basebackup.sgml          |  18 +-
src/bin/pg_basebackup/Makefile               |   2 +-
src/bin/pg_basebackup/pg_basebackup.c        |  62 +-
src/bin/pg_basebackup/pg_receivexlog.c       |  10 +-
src/bin/pg_basebackup/receivelog.c           | 316 ++++------
src/bin/pg_basebackup/receivelog.h           |   3 +-
src/bin/pg_basebackup/t/010_pg_basebackup.pl |   6 +-
src/bin/pg_basebackup/walmethods.c           | 886 +++++++++++++++++++++++++++
src/bin/pg_basebackup/walmethods.h           |  45 ++
src/include/pgtar.h                          |   1 +
src/port/tar.c                               |   2 +-
11 files changed, 1107 insertions(+), 244 deletions(-)