[schema,server] add a security debugging aid (closes #2920304) - Add a DGB_SEC debugging flag (to be used with set_debug/debugged). - Add a context manager (tunesecurity) to filter security assertions. Note: this does not address all read-security mecanisms.

if repo.system_source.dbdriver == 'postgres':
    sql('ALTER TABLE appears ADD COLUMN weight float')
    sql('UPDATE appears SET weight=1.0 ')