By default, retrieving query results row-by-row is enabled.
CMake tries to detect version of PostgreSQL (libpq) used to build SOCI
and if detected version is less than 9.x.x, then the option is
flipped to ON for backward compatibility.
Complements #571
Since the changes of b70a4e8b2f, PostgreSQL
backend is not compatible with PostgreSQL < 9, contrary to the documented
supported platforms in the documentation.
Ideal would be to continue supporting the old versions by default and use
PQsetSingleRowMode() only if it's detected as being available by CMake, but
for now at least allow disabling single mode support manually.
Closes#571.
Heiko Rabe