Set missing charset to MIME message on cron error

issue3522
review1951002
(transplanted from 3fb81bb57a08f38d7889ace13a621ee5ba022838)

--HG--
extra : transplant_source : %3F%B8%1B%B5z%08%F3%8Dx%89%AC%E1%3Ab%1E%E5%BA%02%288
Fix RPC.convert usage to return a copy of args and kwargs

issue3521
review1921002
(transplanted from 2d0b71f9df953047e875ddbd510804474126fad9)

--HG--
extra : transplant_source : -%0Bq%F9%DF%950G%E8u%DD%BDQ%08%04GA%26%FA%D9
Database.list must set manually the flavor

issue3508
review2121002
(transplanted from f18cb8a2ee0c1c826db4259ea4162bb285ef963e)

--HG--
extra : transplant_source : %F1%8C%B8%A2%EE%0C%1C%82m%B4%25%9E%A4%16%2B%B2%85%EF%96%3E