pgsql: Add suport for server-side LZ4 base backup compression.

Add suport for server-side LZ4 base backup compression.

LZ4 compression can be a lot faster than gzip compression, so users
may prefer it even if the compression ratio is not as good. We will
want pg_basebackup to support LZ4 compression and decompression on the
client side as well, and there is a pending patch for that, but it's
by a different author, so I am committing this part separately for
that reason.

Jeevan Ladhe, reviewed by Tushar Ahuja and by me.

Discussion: http://postgr.es/m/CANm22Cg9cArXEaYgHVZhCnzPLfqXCZLAzjwTq7Fc0quXRPfbxA@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/dab298471ff2f91f33bc25bfb73e435d3ab02148

Modified Files
--------------
doc/src/sgml/protocol.sgml | 7 +-
doc/src/sgml/ref/pg_basebackup.sgml | 24 ++-
src/backend/replication/Makefile | 1 +
src/backend/replication/basebackup.c | 7 +-
src/backend/replication/basebackup_lz4.c | 298 ++++++++++++++++++++++++++++++
src/bin/pg_basebackup/pg_basebackup.c | 18 +-
src/bin/pg_verifybackup/Makefile | 1 +
src/bin/pg_verifybackup/t/008_untar.pl | 10 +-
src/include/replication/basebackup_sink.h | 1 +
9 files changed, 349 insertions(+), 18 deletions(-)