(Bug 42659) Rename smw_ids_smw_id_seq

Returns an appropriately quoted sequence value for
inserting a new row. MySQL has autoincrement fields,
so this is just NULL. But the PostgreSQL subclass will
return an integer, and save the value for insertId()

[1] https://bugzilla.wikimedia.org/show_bug.cgi?id=42659#c14

Patch provided by b42@srck.net, Marcin Cieślak
Add Travis postgres run

See [1]

[1] http://about.travis-ci.org/docs/user/database-setup/
(Bug 42659) ERROR: relation "smw_object_ids" already exists

As per suggestions by b42@srck.net, José Antonio use an
empty name as postgres will manage index name generation
if no name is provided.
redefinitions:
  usage_count=$dbtypes[i].
  'i' => ( $wgDBtype == 'postgres' ? 'bigint' : 'INT(8)'.
   To solve unit test issues point in comment 20 of bug 42659.
    Following request in comment 23.
usage_count set to bigint only if when postgres is used.
redefinitions:
  usage_count=$dbtypes[i].
  'i' => ( $wgDBtype == 'postgres' ? 'bigint' : 'INT(8)'.
   To solve unit test issues point in comment 20 of bug 42659.
    Following request in comment 23.
Merge pull request #37 from fallos/postgresql

redefinitions:
Merge pull request #35 from SemanticMediaWiki/postgresql

Postgresql