TO INTEGERS

When a JSON document is converted to string representation,
floating-point values that have no fractional part may be represented
in a format indistinguishable from integers. If the string
representation of such a JSON document is passed through the JSON
parser again, the information that the numeric value was originally
specified as a floating-point value, is lost.

The reason is that the conversion from JSON to string uses my_gcvt()
to format floating-point values, and my_gcvt() does not add a decimal
point if the value has no fractional part.

This patch adds a fractional part to the string representation of
floating-point values in JSON documents if the value has no fractional
part and it is not represented in scientific format. This makes
floating-point values distinguishable from integers in the string
representation, so that they will stay as floating-point numbers if
the string is parsed again.

The patch also makes ST_GeomFromGeoJSON use the same JSON parser as
the other JSON functions. It has used its own custom parser since
bug#19504183 because ST_AsGeoJSON would drop the fractional part of
negative zero (-0 instead of -0.0), and the JSON parser would
interpret -0 as the integer 0 and lose the distinction between
positive and negative zero. Since ST_AsGeoJSON now presents negative
zero as -0.0, no special logic is needed in ST_GeomFromGeoJSON to
preserve negative zeros when parsing the output from ST_AsGeoJSON.

Change-Id: I20508741c981cc2ca2af004757f95ef78558f582