deletes all data in all types for that field
(was introduced earlier in the current cycle,
official 1.6 release is not affected)

#211566 limit data to nodes of the right content type when migrating data from per field to per type tables.

#210683  Clear node values from cache if field information is changed so stale values don't appear in node_load().

 is requested by CCK admin UI (problem with userreviewmodule) - patch by gerd riesselmann

 jimyhuang, sentinelcz

 field' form

#59451 default values now handled by content module unless widget modules opt to handle it themselves. Patch by yched and me.

 are moved from 'node_' to 'content_' namespace)
+ fixes for older 4.7 versions migration path
update.php required !!

 Karen and myself

 (forgot one occurrence)

(+ remove test api hook, since we don't ship with testfile anymore)