Update src/core/session.cpp

Backend is not set properly with connection pool
Added json support for PostgreSQL
Pseudo fixed an issue with debug limit by raising the limit
fixed sqlite3 test
Merge remote-tracking branch 'snikulov/fix_for_15' into issue-15
Merge remote-tracking branch 'upstream/master' into issue-15
Update to Sergei Nikulov's fix for issue #15

Clarify supported sequence of statement::execute(false|true) and
statement::get_affected_rows() calls across all backends:
1. execute(false) and empty destination does not execute statement, but
prepares for subsequent statement::fetch() requests.
2. execute(true)  and empty destination calls requests backend to
execute statement.
3. execute(false|true) causes bulk fetch to destination, with
withDataExchange=false|true ignored.
Moved relevant test to common tests, confirmed it passes for all but
Oracle (get_affected_rows not implemented) and Firebird (I have no means
to test).
Related discussion at
http://sourceforge.net/mailarchive/message.php?msg_id=30312517
Thanks to Sergei who first proposed this behaviour as reliable and
consistent option, yet not intrusive.
Update to Sergei Nikulov's fix for issue #15

Clarify supported sequence of statement::execute(false|true) and
statement::get_affected_rows() calls across all backends:
1. execute(false) and empty destination does not execute statement, but
prepares for subsequent statement::fetch() requests.
2. execute(true)  and empty destination calls requests backend to
execute statement.
3. execute(false|true) causes bulk fetch to destination, with
withDataExchange=false|true ignored.
Moved relevant test to common tests, confirmed it passes for all but
Oracle (get_affected_rows not implemented) and Firebird (I have no means
to test).
Related discussion at
http://sourceforge.net/mailarchive/message.php?msg_id=30312517
Thanks to Sergei who first proposed this behaviour as reliable and
consistent option, yet not intrusive.
Update .travis.yml

Install libmyodbc. Set CMwke property SOCI_ODBC_TEST_MYSQL_CONNSTR.
Update src/backends/odbc/test/test-mysql.dsn

Try minimal DSN settings on travis-ci.org
Update .travis.yml to configure libmyodbc driver
Typo
dpkg-reconfigure firebird2.5-super
Run dpkg-reconfigure as root
playing with binding output parameter as string instead of double
Set up Firebird for tests
Try to fix Firebird connection string
Try to fix Firebird connection string
Clean README
Pull merge