[FIX] orm: rewrite method read() to always check access rights before doing anything else
[IMP] orm: make method is_null() more robust
[IMP] new fields: add method _set_field() in BaseModel
[IMP] new fields: improve field copy, and fix check for non-attribute fields
[IMP] new fields: add new-style fields to interface all columns
[ADD] new fields: add boolean and float fields
[ADD] new fields: add char, text, html, date and datetime fields
[IMP] new fields: refactor methods from_column and to_column
[IMP] new fields: check value format when assigning a field
[ADD] new fields: add binary and selection fields
[IMP] new fields: small refactoring of field methods
[IMP] new fields: add missing option 'translate' on string fields
[IMP] orm: make null instances a subset of records
[IMP] new fields: fix recomputation (spec stored in thread-local instead of scope proxy), and improve tests
[ADD] new fields: add relational fields (many2one, one2many, many2many)
[ADD] new fields: add reference fields + fix small error in selection fields
[MERGE] from trunk
[MERGE] from trunk
[IMP] orm: browse() always returns instances attached to a scope
[IMP] orm: refactor record and recordset instances creation
 - add explicit conversion method to_record(), to_recordset()
 - null(), record(), recordset() return instances attached to the current scope
 - consequently, all BaseModel instances (except the registry one) are attached
   to a scope
 - adapt existing code using those methods