pgsql: Allow to avoid NUL-byte management for stringinfos and use in fo

Allow to avoid NUL-byte management for stringinfos and use in format.c.

In a lot of the places having appendBinaryStringInfo() maintain a
trailing NUL byte wasn't actually meaningful, e.g. when appending an
integer which can contain 0 in one of its bytes.

Removing this yields some small speedup, but more importantly will be
more consistent when providing faster variants of pq_sendint etc.

Author: Andres Freund
Discussion: https://postgr.es/m/20170914063418.sckdzgjfrsbekae4@alap3.anarazel.de

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/70c2d1be2b1e1efa8ef38a92b443fa290a9558dd

Modified Files
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src/backend/lib/stringinfo.c | 21 ++++++++++++++++++++-
src/backend/libpq/pqformat.c | 18 +++++++++---------
src/include/lib/stringinfo.h | 8 ++++++++
3 files changed, 37 insertions(+), 10 deletions(-)