Fixes #13: Export db_fetch_row

Add support for result set retrieving for MySQL and PostgreSQL drivers
and export it to the new Lua SQL API.

tests/t/api_sql_pgsql.t

@@ -0,0 +1,47 @@
+########################################################################
+SQL Lua API + PostgreSQL tests
+########################################################################
+
+  $ . ${SBTEST_INCDIR}/pgsql_common.sh
+  $ . ${SBTEST_INCDIR}/api_sql_common.sh
+  drv:name() = pgsql
+  NONE = 0
+  INT = 3
+  CHAR = 11
+  VARCHAR = 12
+  TIMESTAMP = 10
+  TIME = 7
+  FLOAT = 5
+  TINYINT = 1
+  BIGINT = 4
+  SMALLINT = 2
+  DATE = 8
+  DATETIME = 9
+  DOUBLE = 6
+  
+  NOTICE:  table "t" does not exist, skipping
+  100
+  --
+  NOTICE:  table "t2" does not exist, skipping
+  --
+  1 foo 0.4
+  2 nil 0.3
+  nil bar 0.2
+  nil nil 0.1
+  --
+  bar nil
+  --
+  4
+  301 400 0123456789 0123456789
+  --
+  NOTICE:  table "t" does not exist, skipping
+  1
+  2
+  3
+  4
+  5
+  6
+  7
+  8
+  9
+  10