jdbc: metadata: retrieve database version #106

DatabaseMetaData.

Methods:

• getDatabaseMajorVersion
• getDatabaseMinorVersion
• getDatabaseProductName -- ok; just cover with a test
• getDatabaseProductVersion -- ok; just cover with a test

JDBC support I think should be reported as 4.2 instead of 2.1 (despite it is
not fully compliant):

• getJDBCMajorVersion
• getJDBCMinorVersion