pgsql: to_char(float4/8): zero pad to specified length

to_char(float4/8):  zero pad to specified length

Previously, zero padding was limited to the internal length, rather than
the specified length.  This allows it to match to_char(int/numeric), which
always padded to the specified length.

Regression tests added.

BACKWARD INCOMPATIBILITY

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/cc0d90b73b2e6dd2f301d46818a7265742c41a14

Modified Files
--------------
src/backend/utils/adt/formatting.c    |  114 ++++++++++++++++++++++-----------
src/test/regress/expected/numeric.out |   70 ++++++++++++++++++++
src/test/regress/expected/window.out  |    2 +-
src/test/regress/sql/numeric.sql      |   17 +++++
4 files changed, 163 insertions(+), 40 deletions(-)