pgsql: Speed up conversion of signed integers to C strings.

Speed up conversion of signed integers to C strings.

A hand-coded implementation turns out to be much faster than calling
printf(). In passing, add a few more regresion tests.

Andres Freund, with assorted, mostly cosmetic changes.

Branch
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master

Details
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http://git.postgresql.org/gitweb?p=postgresql.git;a=commitdiff;h=4fc115b2e981f8c63165ca86a23215380a3fda66

Modified Files
--------------
src/backend/utils/adt/int8.c | 8 +--
src/backend/utils/adt/numutils.c | 115 ++++++++++++++++++++++++++++++++----
src/include/utils/builtins.h | 1 +
src/test/regress/expected/int2.out | 13 ++++
src/test/regress/expected/int4.out | 13 ++++
src/test/regress/expected/int8.out | 13 ++++
src/test/regress/sql/int2.sql | 4 +
src/test/regress/sql/int4.sql | 4 +
src/test/regress/sql/int8.sql | 4 +
9 files changed, 157 insertions(+), 18 deletions(-)