Doxygen documentation update:
* Changed alls @addtogroup to @ingroup. @addtogroup adds the comment to the group description, but doesn't add the file, class, function, ... to the group like @ingroup does. See for example http://svn.wikimedia.org/doc/group__SpecialPage.html where it's impossible to see related files, classes, ... that should belong to that group.
* Added @file to file description, it seems that it should be explicitely decalred for file descriptions, otherwise doxygen will think that the comment document the first class, variabled, function, ... that is in that file.
* Removed some empty comments
* Removed some ?>
Added following groups:
* ExternalStorage
* JobQueue
* MaintenanceLanguage
One more thing: there are still a lot of warnings when generating the doc.
* Adding ApiQueryBase::addJoinConds() as wrapper for Database::select()'s $join_conds parameter
* Migrating query modules to addJoinConds()
* Using implicit join rather than INNER JOIN in ApiQueryBacklinks
* Using FORCE INDEX (times) on logging table in ApiQueryLogEvents; although MySQL 4 seems to pick this index automatically (evidenced by the fact the WMF servers are still alive), MySQL 5 doesn't and filesorts
* Replacing LEFT JOIN with implicit (inner) join in ApiQueryContributions: revisions without a corresponding page table entry shouldn't be shown anyway
* Added ApiQueryBase::addJoin() which provides a cleaner interface to construct JOIN queries. Behind the scenes this still uses the old, ugly way, but it'll be easy to rewrite when/if the Database class gets its own function for JOINs
* Used addJoin() in query modules where necessary
* Removed FORCE INDEX (rc_timestamp) from ApiQueryRecentchanges: it's nigh impossible to integrate with addJoin() and it doesn't seem to be necessary anyway (my MySQL instance automatically chooses rc_timestamp)
