Improve Database related documentation a bit

- $wgDBport is also for MSSQL
- "type" key of $wgDBservers is not only "mysql" and "postgres"
- Note that $wgDBssl, $wgDBcompress and $wgDebugDumpSql only
  work in certain cases and mention how to emulate them otherwise

Change-Id: Id863da8c87308d06e0070877ac0af26d03be4faf
Merge "Improve Database related documentation a bit"