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
------
master

Details
-------
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(-)