[COMMITTERS] pgsql: Refactor SHA2 functions and move them to src/common/.

Refactor SHA2 functions and move them to src/common/.

This way both frontend and backends can use them. The functions are taken
from pgcrypto, which now fetches the source files it needs from
src/common/.

A new interface is designed for the SHA2 functions, which allow linking
to either OpenSSL or the in-core stuff taken from KAME as needed.

Michael Paquier, reviewed by Robert Haas.

Discussion: https://www.postgresql.org/message-id/CAB7nPqTGKuTM5jiZriHrNaQeVqp5e_iT3X4BFLWY_HyHxLvySQ%40mail.gmail.com

Branch
------
master

Details
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http://git.postgresql.org/pg/commitdiff/273c458a2b3a0fb73968020ea5e9e35eb6928967

Modified Files
--------------
contrib/pgcrypto/.gitignore      |    4 +
contrib/pgcrypto/Makefile        |    9 +-
contrib/pgcrypto/internal-sha2.c |   82 ++--
contrib/pgcrypto/sha2.c          |  992 -------------------------------------
contrib/pgcrypto/sha2.h          |  100 ----
src/common/Makefile              |    6 +
src/common/sha2.c                | 1006 ++++++++++++++++++++++++++++++++++++++
src/common/sha2_openssl.c        |  102 ++++
src/include/common/sha2.h        |  115 +++++
src/tools/msvc/Mkvcbuild.pm      |   20 +-
10 files changed, 1297 insertions(+), 1139 deletions(-)