[FIX] correct two problems with domains:
[FIX] correct two problems with domains:

- an empty domain is treated as equivalent to []
- AND and OR symbols are introduced more carefully
gisce/openobject-server,MarkusTeufelberger/openobject-server,MarkusTeufelberger/openobject-server,gisce/openobject-server,splbio/openobject-server,vnc-biz/openerp-server,ovnicraft/openerp-server,MarkusTeufelberger/openobject-server,splbio/openobject-server,vnc-biz/openerp-server,gisce/openobject-server,ovnicraft/openerp-server,splbio/openobject-server