Added rdbms::PooledDbConn though it still not used beyond testing

catalogue/CatalogueFactory.cpp

catalogue/CatalogueFactory.hpp

catalogue/CatalogueFactoryTest.cpp

catalogue/CatalogueTest.cpp

catalogue/InMemoryCatalogue.cpp

catalogue/OracleCatalogue.cpp

catalogue/OracleCatalogue.hpp

catalogue/RdbmsCatalogue.hpp

catalogue/SqliteCatalogue.cpp

catalogue/SqliteCatalogue.hpp

rdbms/CMakeLists.txt

rdbms/DbConnPool.cpp

rdbms/DbConnPool.hpp

rdbms/DbConnPoolTest.cpp

rdbms/PooledDbConn.cpp

rdbms/PooledDbConn.hpp

scheduler/SchedulerTest.cpp

...stor/tape/tapeserver/daemon/MigrationReportPackerTest.cpp

tapeserver/castor/tape/tapeserver/daemon/ProcessForker.cpp

xroot_plugins/XrdCtaFilesystem.cpp