Direct converting numeric types to bool

[n . zhuchkov]

Attached patch allow direct convertion of numeric types to bool like 
integer::bool.
Supported types:
 - smallint;
 - bigint;
 - real;
 - double precision;
 - decimal(numeric).
This functionality is helped with migration from Oracle.

--
Nikita Zhuchkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company