[IMP]: allow binary function fields to directly return size.
[IMP]: allow binary function fields to directly return size.

As used in document, function fields could have a shortcut method to
return the size instead of the contents. If done so and return a number,
use that instead.

ovnicraft/openerp-server,splbio/openobject-server,gisce/openobject-server,MarkusTeufelberger/openobject-server,gisce/openobject-server,MarkusTeufelberger/openobject-server,MarkusTeufelberger/openobject-server,vnc-biz/openerp-server,ovnicraft/openerp-server,xrg/openerp-server,vnc-biz/openerp-server,splbio/openobject-server,gisce/openobject-server,splbio/openobject-server,xrg/openerp-server