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
Ignored ide files

Copied empty backend skeleton to db2 backend

Added DB2 detection and building

Implemented session backend calls
Added DB2 backend
Added better error message for describe column
Added string bulk operations test
Made connect string compatible with ODBC connect string
Made connect string compatible with ODBC connect string
Fixed invalid autocommit setting
Turned autocommit to on by default
Fixed invalid parameters binding
Added statement unbinding before statement handle cleanup
Ignored ide files

Copied empty backend skeleton to db2 backend

Added DB2 detection and building

Implemented session backend calls
Added DB2 backend
Removed x_unsigned_log from the db2 backend.
Fixed libdir detection for db2
fixed sqlite3 test
Merge remote-tracking branch 'snikulov/fix_for_15' into issue-15
Merge remote-tracking branch 'upstream/master' into issue-15