pgsql: Add #include <float.h> --- guessing the lack of this is why

Log Message:
-----------
Add #include <float.h> --- guessing the lack of this is why Windows
machines are all rejecting isinf() calls in this file.

Modified Files:
--------------
pgsql/src/interfaces/ecpg/ecpglib:
execute.c (r1.91 -> r1.92)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/ecpglib/execute.c?r1=1.91&r2=1.92)