Fix on One2Many on_change when field value is not defined for current record

issue4258
review12641002
(grafted from 0e4297b7a3881341d8da2d60b6e1db46b0e6aab1)

--HG--
branch : 3.4
extra : source : 0e4297b7a3881341d8da2d60b6e1db46b0e6aab1
py2app doesn't have site.USER_BASE

issue4269
review14591003
(grafted from 8cc4a3d6e5f0a1262984a2e8277413b840f326d7)

--HG--
branch : 3.4
extra : source : 8cc4a3d6e5f0a1262984a2e8277413b840f326d7
data2pixbuf fails if data is None

because len is called on data

issue4265
review13631002
(grafted from 82a611d1b9a64381ac416e71ffecff7533e2ff9b)

--HG--
branch : 3.4
extra : source : 82a611d1b9a64381ac416e71ffecff7533e2ff9b
pack at the end the entry of Many2One to fix layout of Reference widget

Restore pack_end of entry removed in changeset 89af0b300c3f

issue4293
review13671002
(grafted from 4019f404f90803ca4e1863ba26e78b94c2389068)

--HG--
branch : 3.4
extra : source : 4019f404f90803ca4e1863ba26e78b94c2389068