[FIX] expression: properly care for implicitly defined m2m fields used in search() domains
[FIX] expression: properly care for implicitly defined m2m fields used in search() domains

Now that m2m fields may be defined without explicitly
specifying the name of the relationship table and its
foreign key columns, all access to these internal
names should be done via m2m._sql_names().
This seems better than lazily initializing these
internal names and hoping that nothing accesses
them before the init.
splbio/openobject-server,splbio/openobject-server,MarkusTeufelberger/openobject-server,splbio/openobject-server,ovnicraft/openerp-server,MarkusTeufelberger/openobject-server,vnc-biz/openerp-server,gisce/openobject-server,gisce/openobject-server,MarkusTeufelberger/openobject-server,gisce/openobject-server,vnc-biz/openerp-server,ovnicraft/openerp-server