Add sql update script which regenerates the ref_count for all artist_credits.
Schema 18: Setup new upgrade script and add tools for dropping/recreating the track table.
Merge remote-tracking branch 'warp-bitbucket/update-artist-credit-refcount' into schema-18

* warp-bitbucket/update-artist-credit-refcount:
  Add sql update script which regenerates the ref_count for all artist_credits.
Schema 18: add artist_credit.ref_count fixes to upgrade.sh
Schema 18: don't dump replication_control
MBS-6357: rename/fix track2013 and medium2013-named indexes/constraints (also, fix upgrade.sh whitespace)
MBS-6357: ALTER INDEX IF EXISTS is only postgres 9.2
MBS-6357: s/(medium|track)_2013/${1}2013/
Schema 18: Update DBDefs.pm.sample
Schema 18: Add ON_ERROR_STOP to refcount script
Schema 18: Import luks' fast artist-refcount process, to be integrated
Schema 18: flesh out the faster refcount fix and integrate with upgrade.sh
Schema 18: remove cruft
Schema 18: remove warp's slow refcount fixing script
Schema 18: fix up the exclusion of replication_control in specific dumps
Schema 18: rename indexes unconditionally and ignoring errors, for imports done on schema 17 fullexports
Schema 18: drop medium_cdtoc_fk_medium if exists, ensure artist-credit refcounts are plain integers, not bigints.
Schema 18: vacuum analyze at end of script
Schema 18: don't miss the artist_credit.name FK
Download track table dump before start the upgrade, and verify track table dump download.